Drones would work, if drones worked.
Unfortunatly they can't be fleeted, and won't warp together. So it would be next to impossible to make any attacks.
Unless I made the Risk map a single system with 42 planets, and placed damaging storms to keep you from moving except between planets that I wanted you to move between.
THen you could use drones and I could tweak the resource numbers so you could build a certain number per turn but put them where you wanted. Except that you could only build them in multiples that the build queue allows. 1, 5, 10, etc.