Apple - As an iOS Developer, how can I avoid upgrading to Lion?

You really can't. Unless you skip to Mountain Lion. It's one of the blessings and curses of being an Apple Developer and that is that you must stay current, or you're out of the game for both iOS and Mac Development.

To use the latest bells and whistles for the next OS releases, you are really going to be bound to Apple's software and hardware requirements for those tools, otherwise you will find yourself spending too much time hacking together your build tools, instead of making forward progress.

Get yourself a copy of VMware Fusion and run your various development OS virtually. As a developer this is a critical step to ensure you have the ability to support older and newer OS without needing dedicated hardware for each image.

On rare occasion you will want to move a specific image to an external drive and boot 100% in that OS (or restore that image on to an internal drive) - but for most situations the penalty for running virtually isn't something that sends a particular setup over the brink to being too slow.