I've just added a tutorial to my website with links to custom script libraries which allow multiple level undo/ redos in a single click via a custom palette. Below is a custom palette I create in Painter 7;

A Multiple Undo-Redo Custom Palette for Painter Classic 1 Through Painter 8.1.

I have designed the individual script icons such that those with a black background perform undo operations, and those with a white background, redo operations. The level of undo is indicated by the number on each icon. For example, if I make two separate brush strokes on my canvas, then click the '2' icon with a black background (from the custom palette), the two strokes will be undone. Clicking the '2' icon with a white background will return the two strokes (as would clicking the '1' icon with the white background twice).

Here is the tutorial page. The associated scripts can be downloaded on the same page.