Make it so you can't transfer to Fatman or JC UNLESS you are already established there i.e. a level 50 or legacy level whatever. It won't really increase the population since the person is already there and doesn't shaft folks who quite frankly the only reason they are still playing is becuase they want to bring thier old chars to thier new home.
Another poster said it but I'll repeat it. If I rerolled from a dead server to Fatman and then they allow transfers from the old server to a server other than Fatman what's the point? I am not gonna leave Fatman since I've already made a new home there. Not to mention the uncertainty of the destination servers being much better then the old dead servers are now.
And you'll have the opportunity to do exactly that at a later time, for a fee, just like other games.
What you and the dude above don't seem to understand is that this consolidation is ONLY meant to fix population issues, not to enable you to go to wherever you want to go. The "choice" you want is a later step, that, not surprisingly, comes later.