Things like this are what make phones with physical keyboard awesome. Granted, this may be possible with an all touch screen device but it will surely be a tougher feat to accomplish. Game Gripper has successfully converted a Motorola Droid into a classic controller.
For only $14.99 this can be yours. It has been tested with GameBoid, Nesoid, and SNesoid. If I had a droid I would be all over this. Nesoid is one of my most used apps and this controller will make playing a breeze and more enjoyable. Head over to Game Gripper and purchase yours now.