Following on from the "Turbo in a bottle" thread, I did some research and found the electric turbocharger I mentioned (it's manufactured by TurboDyne). You can see it here:
http://www.turbodyne.com/product2.html
It's actually quite clever! The electric motor sits on the shaft between the turbine and the impeller, and it is able to keep the turbo on boost when there isn't enough exhaust gas flowing to maintain sufficient shaft speed. Once the turbo is able to spool up of its own accord, the motor becomes a generator which replaces the power drained from the battery (and it appears this thing can drain a significant amount of power). They claim this eliminates the need for a wastegate in some cases.