Add-ons don’t display in grouped product page

Hi, a client of mine uses this plugin to add some payed options on products, but the shop also uses Grouped products now and the add-ons don’t show on the grouped product page, only on the simple product pages. Is there a solution for this ?

Adding add-ons to the grouped product is not an option because the add-ons are specific to the “sub-products” of the group and can’t be applied to the whole group.
Or is there another plugin that does this ?

Thank you