Long ago I had this same idea. To test it I put a cheap fan (one of those fans they sell for truckers to put on their dash) behind the right rad. It wasn't a great install, but it made no measurable difference on the ground and after a short flight the fan blades had completely broken off. I'm sure you would see better results with something like this
But I'm still not convinced it's worth it. The work that I've done with improved ducting seems to have made a world of difference and my temps are staying under control even with extensive ground testing. The temps get hottest after shutdown which I never experienced before (more in a separate post).
However I would be curious to know the results of testing with a proper fan.
You are in Australia, correct? Davies Craig is a company from down under and I'm using their EWP's in my plane. They seem good to talk to, so give them a call and tell them what you plan on using it for.
Todd --- It's a good thing I have no neighbors close enough to see me or they'd think I went nuts today, taxing circles in my driveway.