At the start of the skirmish, choose a Unique allied character. That character may spend Darth Sidious's Force points as if they were its own.
During setup, if you have Darth Sidious in your squad, choose a Unique allied character in your squad. The chosen ally can spend Force points from Darth Sidious as if they were its own. That ally doesn't have to have a Force rating, but if it does, it cannot spend its own Force points on the same turn.