Since stacking is a huge problem in the operation/hosting of these games, the losing team must have some sort of compensation for the time they spent playing.

I was thinking that perhaps they could get a percentage of the experience they would normally get for the damage they have done. This would only be for the team that loses.

Example:
I'm on the losing team, but in the losing effort I managed to do 200k damage, I should get a reasonable amount of experience, a percentage of the experience I would receive in a typical game.

Having this in place would not make the losing team retreat, and give them the incentive to prevent the other team from running up the score and getting experience they haven't earned.

This is by no means a perfect solution, but the difference between winning and losing has been pretty much removed from regular games, why not make this simple modification and credit people for playing out the full game and doing a good deal of damage to prevent the other team from running away with the game, and sitting afk as an alternative.