Freeing up a character without spending doughnuts.

In case you weren't aware, you can also store the building/decoration that the character is using for the task to free them up, too. That's useful for Homer or Lisa. For Homer, I try to keep him in the Ice Cream skin since the truck is storable. Lisa's a little trickier, but if you're careful you can make it work.

Then the only problem is characters without buildings with tasks at the Simpson's house.