excludeClipRegion question

Is it possible to reduce a clip region by anything other than a rectangle, as is done in excludeClipRegion()?

I’ve got a trapazoid that I’d like to fill with various colors, and it would be much easier to exclude the triangular pieces at the ends, and have the clipping region take care of the drawing outside of the bounds than to calculate exact paths.

Is there any difference between reducing the clipping region and drawing an opaque triangle over the areas I want to clip after doing all my rectangular fills?