The trick is to point Redsn0w 0.9.8b1 to iOS 5 beta firmware file. MuscleNerd of the iPhone Dev Team has also confirmed this on Twitter:
5.0b2 can be jailbroken w/redsn0w from 2 wks ago (must point redsn0w at 5.0b1 IPSW)..devs ONLY please
the “keep pointing at beta1 IPSW” trick should work for all the betas, due to the way redsn0w works. Unlockers stay away!
Redsn0w 0.9.8b1 supports the following iOS 5 devices:
Redsn0w 0.9.8b1 supports a tethered jailbreak, which means that you need to connect your iOS device to the computer on every reboot.
Please don’t forget to backup your iOS device before you proceed to jailbreak it. You can refer to this post for instructions on how to backup your iOS device.
As always, let us know how it goes.
[via Twitter (MuscleNerd)]