J2Store add quantity input and add to cart button for each product option

Question

I'm using J2Store and would like to display a "quantity input" and an "add to cart button" for each product option so that I can get rid of the radio button completely. This way, clicking the add to cart button will indicate that that product option is selected, instead of clicking a radio button and then the add to cart button.

Right now I have the elements added to each option line, but they aren't functioning properly. If I input a quantity other than "1" it still only adds one item to the cart. Attached is a screenshot of what I have so far.

As per @Lodder 's request, here is the relevant code from my addtocart_option.php file:

<?php if ($option['type'] == 'radio') { ?>
            <div id="option-<?php echo $option['product_option_id']; ?>" class="option">
                <?php if ($option['required']) { ?>
                    <span class="required">*</span>
                <?php } ?>
                <b><?php echo $option['option_name']; ?>:</b><br />
                <?php foreach ($option['optionvalue'] as $option_value) { ?> <!--loop through product options-->
                    <div class="option-line"><!--HEYOOO! HERE'S YOUR PRODUCT OPTION LINE!-->
                        <label for="option-value-<?php echo $option_value['product_optionvalue_id']; ?>"><?php echo $option_value['optionvalue_name']; ?>
                        <!--TAX STUFF, DON'T TOUCH!-->
                        <?php if ($option_value['product_optionvalue_price'] > 0) { ?>
                            <?php $tax = $this->tax_class->getProductTax($option_value['product_optionvalue_price'], $this->item->product_id); ?>
                            <?php  echo J2StoreHelperCart::dispayPriceWithTax($option_value['product_optionvalue_price'], $tax, $this->params->get('price_display_options', 1)); ?>
                        <?php } ?>
                        <!--/TAX STUFF-->
                        </label>

                        <input <?php echo $checked; ?> 
                        type="radio" 
                        name="product_option[<?php echo $option['product_option_id']; ?>]" 
                        value="<?php echo $option_value['product_optionvalue_id']; ?>" 
                        id="option-value-<?php echo $option_value['product_optionvalue_id']; ?>" 
                        />
                        <!--QUANTITY INPUT FOR OPTION-->
                        <div id='product_quantity_input_<?php echo $item->product_id; ?>' class="product_quantity_input">

                            <input 
                            type="text" 
                            name="product_qty" 
                            value="<?php echo $item->product_quantity; ?>" 
                            size="3" 
                            />
                            <?php if(isset($item->item_minimum_notice)):?>
                                <br />
                                <small class="j2store-minmum-quantity muted"><?php echo $item->item_minimum_notice; ?></small>
                            <?php endif; ?>
                        </div><!--/"product_quantity_input"-->

                        <!--ADD TO CART BUTTON FOR OPTION VALUE-->
                        <div id='add_to_cart_<?php echo $item->product_id; ?>' class="j2store_add_to_cart" style="display: block;">
                            <input 
                            type="hidden" 
                            id="j2store_product_id" 
                            name="product_id" 
                            value="<?php echo $option_value['product_optionvalue_id']; ?>" 
                            />
                            <?php echo JHTML::_( 'form.token' ); ?>

                            <input 
                            type="hidden" 
                            name="return" 
                            value="<?php echo base64_encode( JUri::getInstance()->toString() ); ?>" 
                            />

                            <input 
                            type="submit" 
                            name="product_option[<?php echo $option['product_option_id']; ?>]"
                            value="+" 
                            class="j2store_cart_button btn btn-primary" 
                            id="option-value-<?php echo $option_value['product_optionvalue_id']; ?>" 
                            />
                        </div><!--/"add_to_cart"-->
                    </div><!--/"option-line"-->

            <?php } ?>
            </div><!--/"option"-->
        <?php } ?>

Any help or suggestions would be most appreciated!