Gas generator?  DC to AC inverter run from your car?  Maybe a battery jump box found at Checker/Auto Zone/Schuck's Kragen?  Or use them unpowered just as practice pads.

I wouldn't want to hook up a small generator just for this but there are some options.  One, definately not ideal, you could get an inverter and us a 12v battery (probably a marine/deep cycle battery).  If you don't know anything about this stuff, get someone who does to help you - you could get hurt.  Radio shack sells inverters for converting 12V car dc to 120V ac so people can play their games, use their pc in the car.  You would also need a charger to charge up the battery after your sessions (do you want a battery/charger sitting in your apartment?).  I don't know how long the battery will keep the Vdrum going but it's a simple calculation if you know the amp draw on the vdrum.  One concern is that you do not want to damage the Vdrum so you should have either a low voltage cutout on the inverter or a volt meter on the batter so you don't try playing when the battery runs low.  Again, get someone who knows about this stuff to help.  By reading this you explicitly release and hold harmless all cafe members if you should get hurt or cause damage to equipment 

Some folks have built sound/vibration isolating risers for their apartments. I think if you search the site you'll find some discussion on this topic.