Oops - what I mean is, mass bombing of cities alone never forced a country to surrender. Eg: Battle of Britain. Certainly being bombed demoralises a population, but it won't force a surrender unless the war is already lost.
Here's some ideas (I don't think they're anything new though)
To encourage people to fly bombers, make it necessary to bomb industrial targets - new planes would take longer to develop, ammunition and fuel would lower in quality as well as supply.
Make it such that factories will only be damaged signifigantly by a large number of bombs hitting in a short time period, so that fighters alone would not be able to carry the neccessary bomb load, but several bombers could.
Constant pressure on city targets would lower morale through constant heavy attacks, so that a single "bomber rush" attack when the enemy is down to a few airfields would have little effect, but constant raids would have lowered morale enough that the enemy would surrender.
We also need some sort of command structure - so that pilots know what to do. My (limited) experience of WB was a disorganised bunch of pilots all wondering what to do next.
[This message has been edited by juzz (edited 09-14-1999).]