Build an Obelisk then place it. Before it reaches the end of its building cycle click on it and hit S.

The Obelisk will appear without the power requirement bar going up (there is on drawback:

you can't build more buildings unless you have a second Construction Yard).

ENDLESS MINI GUNNERS-For swarms of Mini gunners, you need a Guard Tower.

Sell the Guard Tower then quickly click on it and hit S.

The Mini gunners will pop out but the building will stay.

This only works on Guard Towers and believe me, its useful.