How to set up wireless bridge on same subnet?
I've had the same question, but from the other point of view. I wasn't aware of ifconfig (kinda new to this stuff).
I think I got it working by doing it the other way round.
I first had OS X share my internet over wifi (via sharing preferences)
Then with ifconfig, you'll see that OS X creates a bridge100 (or something)
I set the IP manually like you did on that bridge
and then I add my network connection supplying the internet access.

Not entirely sure whether it works perfectly, at first glance, everything works OK, but who knows....