Hrmm... b/c you plan on using a little exhaust-type setup, you might be able to make the thing pretty much fly!
With the exhaust style setup, as long as you tune everything just right you could get it to work great ... rather than having the exhaust parallel to the ground at the end, have it pointing about 5 degrees up for some down force (it's an XMod, not an Airplane) and it might work good. Also, don't go to small on tubing, backpressure would make it explode (bye bye, poor XMod). I'd love to see how it turns out