Checkboxes for custom fields

Vendors need to be able to select multiple options for custom fields I have in VM when they add a product to their store. I purchased a plugin (customfieldsforall) for VM that allows you to use checkboxes in the custom fields instead of only lists. This works fine in the backend but the custom fields don't show up on the FE when a vendor adds a product. I tried to modify the php file in addproduct adding a case for field type "E" but am having no luck. Any chance you can help?