power somewhere and you're done. You might have problems with it bumping the buttons on the HU this way though, so get some rubber feet to attach to the HU so it clears. If you attached it with magnets or velcro somehow you could also take the tablet with you when you got out of the car.
Again, its ghetto, but if you did it right it wouldn't be THAT ghetto. I sorta doubt you'll find a double din mounting kit for a tablet as they vary in size a lot and I dont see a lot of market for something like that.
Not sure what you expect in terms of professionalism when you're not willing to fabricate anything though. I'd say just take a stab at making something custom, just go find yourself a 2nd dash bezel at a junkyard so if your project goes horribly wrong you don't end up with a ****ed up car.