Isometric Sprite with an Inclined Side

Hi,

I’m familiar with how to make an isometric cube and other art that involves the same scale, skew, rotate routine.

However, if I want, for example, the left side to be inclined 15, 30, or 40 degrees, how would I achieve this? Another way to imagine what I’m trying to achieve is moving the bottom edge of the left side away from the cube.