That's a good question, I'm trying to work it out too... here's what I've found so far:
Leave in the carboy and Purge headspace with Co2
Transfer into 3gal Carboy (stir-it up first if you want some yeast cake)
Add something inert and food safe to fill up the extra space (sanitized marbles or something?)
Transfer into a few smaller 1gal carboys (juice jug, etc)
I'm kinda lazy so I'll be trying option #1 first.
I'm looking forward to hearing some other ideas out there.