Custom Fill Pattern

[MacGyver]

So I read the article VisGuy has on the advance fill techniques.
http://www.visguy.com/2009/09/09/visio-tutorial-advanced-fill-effects/

I followed method two in the article using the bitmap method.  Question is can i create a custom fill pattern of two colors that intelligently splits a rectangle in two triangles and applies colors accordingly.  Basically i would like the angle of the pattern to change depending upon the size of the rectangle.  Some of the standard patterns included with visio do this, can I create custom patterns to do this?  Much better to show you what I'm trying to do, and what is happening