Add a feature that will allow you to move the pivot point of a shape anywhere by dragging it. This will make skeletal animation possible.
If you're talking about standard animation then it's tricky but possible. You don't however need to have a pivot point. You can also animate frame by frame, where each slide is set to play instantaneously after the former. By adding another shape on top of where you'd want to pivot, make sure that the bit underneath your new shape is in the same place and rotate/translate to fit that adjustment. It gets some getting used to but it's a surprisingly painless technique should you know what you're doing.
Elijah Ingram commented
As David Smith commented, skeletal animation is fully possible, though having a visual representation of where the pivot point is would be quite nice to have.
David Smith commented
You can bodge this by grouping the object you want to pivot with another shape that has no outline and full transparency. Then move the 'invisible' object away from the original so that the vertical and horizontal centre of the whole group is roughly at the point where you want it to pivot.