In other words, you can become a member from buying any one product, and then "add" other products to your account which will then open without the need for you to go to another site or create additional logins. Otherwise, they appear locked.
Each would have its own sales page, so people could "come in" on any product.
I saw Rich Schefren did this on his site:
Can this be accomplished with any of the popular packages? Profitstheme? OptimizePress/Wishlist? Other solutions?