I like to use the jig saw upside down in a parallel vice. That’s really handy for (almost) precise non straight cuts.
The problem with smaller pieces was, that the window around the saw blade in the base plate is so big, that there is not always enough support on both sides. The result is an uncontrolled jumping of the work piece.
To eliminate that I made a simple baseplate out of aluminum. It’s screwed on top of the stock one. So it can be easily removed when I want to use the jig saw in a conventional way.
Jigsaw base plate for cutting small pieces upside down