"I think this another one of those constraining rules that stifle creativity in bonsai. The Sistine Chapel's ceiling was the frame, the creative project was to fill that frame. Why not?"
HA! The Sistine chapel wasn't a frame. It was a canvas. A tree is similarly the canvas. You fill the canvas with work, not the frame...
The thought that patience is "stifling" is kind of stifling in itself. Patience constrains, sure, but restraint and self control aren't bad things. The desire to instantly fill the pot, just because its nice (not to mention expensive) is something to be resisted. Simply plunking any old tree into it that's "close" to what the pot suggests would ultimately produce a composition that makes the tree and pot look silly.
Why wait? Go out and find a tree that fits the pot. Sure, go ahead, not a problem. However, finding one that ACTUALLY fits is really the issue. That search can take days (if you've got access to great material), or it can take years. The issue isn't filling the pot. It's filling it with something worthwhile.