Under-populated? No worries, spend less time dead.

[Acaila]

Take an empires population, divide it by 33.333333(yaddayadda), multiply by the standard respawn timer to get a new respawn timer.

pop\33.3*stdRespawn=newRespawn

So if NC had 50%, TR 30% and VS 20% and say the you take a player from each empire who just died and would normally have a 30 sec respawn timer.

The NC: 45 secs
The TR: 27 secs
The VS: 18 secs

Obviously the current minimum and maximum respawn timers would still be in effect. This balances pop imbalances by forcing whoever has the highest global population to spend more time dead.