Playstation Plus: Buy game from "Instant Game Collection"?

I'm a new subscriber of Playstation Plus and I've downloaded a few games in the "Instant Game Collection" that are offered free right now to subscribers. I know that I can play these games as long as I maintain a valid Playstation Plus subscription.

However, what if I want to really purchase one of these games digitally (not on disc) so that I can play it even after my Playstation Plus subscription expires? I do not want to wait till my subscription expires to purchase one of these "free" games because there may be some good deals in between to buy these at a cheaper price (instead of looking for a good price after the subscription expires).

Unfortunately, you can't do that directly off the PlayStation Network Store, since the buy option won't be available for games you own through PS+, only after your subscription has expired will that option be available again.

However, you may be able to purchase the full games through third party sources. For example, GameStop offers download codes for PSN games that can be redeemed on the PSN Store. I assume that if you redeem a code for a game you only "own" through PS+, you'll own it permanently (you can check the game's information in the XMB and see if it has an expiration date).

I cannot confirm this method 100% as I haven't tested it myself, so try at your own risk.