I recently stumbled upon a GameDev.net thread regarding shader based antialiasing and they work!
There are several implementations, some faster and cheaper, some more advanced. And here are some of them in BGE
I`ll play with them a little more, maybe I can come up with something new
My favorite is DLAA at the moment(though not yet fully implemented). SSAA is the fastest one.
comparison screenshot (from upcoming demo ):
an example blend is in this thread: