So, I disassembled the dust bin to extract the vacuum fan. Then, using the all-pupose attachment implement (aka duct tape) I secured the fan to the hovercraft.
Next, I had to find a way to turn on just the fan motor. I tried the SCI Tester program that you can get from the RooTooth people, but it only ran in safe mode (which was a problem because it didn't override the cliff sensors). Next, I tried the Microsoft Robotics Studio, but I couldn't get it to connect (I'll have to dig more). Finally, I found a program by "Black 64" - http://www.roombareview.com/chat/viewtopic.php?t=6941 that did the trick. I could send the 132 command (Full Mode) and then individually control each motor regardless of the cliff sensor status. The whirr of the motor sounded quite good at this point.
My first attempt was to just switch the leads and see if that switched the fan direction. Unfortunately, the circuit was smart enough to overcome that and continued to run in the "correct" direction which was the wrong direction for my intent. So my fan was sucking instead of blowing. So, I detached it and reoriented it so that it would then blow. Now set for a first flight.
So, it turns out that the Roomba fan motor isn't powerful enough to even lift the wooden platform off the ground, much less fully burdened with a 10lb Roomba. So I'll need to start investigating fan options and looking at stripping some weight off the Roomba. This is no longer going to be something that others could do without affecting the performance of their bot.
Images of the latest activity can be found here: http://www.flickr.com/photos/27513500@N04/sets/72157605657201637/