I'm with you. I've seen enough rear-endings that I always stay at least a few seconds back...
Here's what my drivers ed taught me to try to get tailgaters to back off, and it actually works more often than not.
Tap the brakes just enough to activate your brake lights (without actually slowing down--leave your other foot on the accelerator. You just want to warn them, not get rear ended... Especially don't slow down if they're on a cell phone or dealing with some other distraction!).
A few tries of that should concern the person behind you enough to get them to back off -- either because they understand that's code for back off, or because they don't know what the crazy lady in front of them is doing.
(if it doesn't help, just give up. either let them pass, or do your best to ignore them...)