Talk to him and see if he'll go halfsies on it. It's the best deterrent to behavior that will damage the unit, and you don't have to be a complete douche about the situation. If he's not interested, then later inform him that you are buying it and if he's still not interested in going in on it, then he can't use it and monitor it's usage. If he starts using it, restort to the simple VoltBolt or whatever to stop him from using it. He'll realize he got busted and cut it out. You don't have to be a douche to beat the douche.
I have no idea why someone who is renting is willing to put down the several hundred $'s into (relatively) permanent appliances. They aren't fun or easy to move, and at a rental property, you aren't likely to be there for the lifespan of the appliance. Honestly, it sounds to me like the landlord is just looking for an excuse so he doesn't have to put in a washer/dryer, and hoping to get a pair on the cheap when you leave.