Think creatively. Create a humble bundle 4 app with an interface that allows you to play any of the included games within the app. Have it be a free download with IAP of various amounts to allow people to show their support that way.
Apple's 30% cut would be a downer, but it could be done.
Didn't Capcom did something like that with their old console games? I think they had an app with some demos and were selling their games as IAP. Might work!
It could be three apps with buttons to activate the purchase in the other apps (or one could create a separate pasteboard just to store activation data)
Apple's 30% cut would be a downer, but it could be done.