AHA! Figured out a tribute system with current game mechanics.
Defeat an alliance.
Demand Attack Heroes from that alliance or death.
Say the terms would be 5 attack 200 heroes every week, or even like an attack 300 hero.
The heroes can be delivered via the other alliance repeatedly attacking with that hero by a scout to the members you want the heroes to go to. After a few attacks and the hero loyalty going down, your member should capture the hero.
The demands, and how the heroes are distributed would obviously vary.
Forcing your defeated enemies to level up and transfer attack heroes, would be a easy way to keep their forces in check, because the only good way to lvl attack heroes is lvl 10 NPCs, thus it will limit their forces, also it strengthens your own alliance, because it allows your members to have access to good heroes, and can easily boost up newer members to allow them to have heroes that can farm lvl 10 NPCs, to get over that certain awkward roadblock when your hero is around 140ish attack.
Basically, make your defeated enemies level up attack heroes for you, thus controlling their forces and making your own members stronger.
An Easier, an more palatable tribute.
Take over a nearby valley of tributee.
Reinforce with truck(s) with reasonable tribute resources
Allow tributee to take over valley and when truck with resources...
I know gold isn't what it used to be, but it is a more than reasonable tribute for most people...