Plugin: Product Password
This plugin allow you to hide some products on signup page unless user provided valid product code during sign up.
Plugin Setup:
Specify some Product Password within product settings aMember CP -> Products -> Mange Products -> (edit)
Edit your signup form and split to two pages (use Page Separator brick to do it)
- on first page put brick 'Product Code'
- on second page put brick 'Product'
Plugin will remove products with code from list unless user specify correct one on previouse page.