Here's a thought...
Maybe have a contest of sorts but do it via a "kit". Basically a bunch of raw parts and anything built MUST use the ONLY the parts in the kit. It would be a great way to get a COTS kit that could be worked into the existing stock of Estes parts.
The once the kit is done, you could have a contest for "grade school" kids to design the color scheme and decals. On the website there would be a template that kids could print out and color in, or "computer enhance" etc.
Sort of a participatory build via long distance.