After a few months off this project, spending my time doing work and summer stuff, I'm back to my RepStrap project. I ended up ordering a custom extruder part from Shapeways that cut a big headache out of my design. It's a bit of a cheat, perhaps, but it solved my chicken and egg problem.
I just ran the first few layers of PLA, and it's looking good. still have some feed issues I'll have to work on, but there is no warp at all. I should be able to make good progress, and perhaps some full prints, this week.