That is a device called a "chorded keyboard" been around for decades.
Some background:
http://trevors-trinkets.blogspot.com...keyboards.html
But the idea of using the existing 5-way button on the device, that is a good one.
Other 5-finger keyboards:
http://www.google.com/search?q=five+...w=1099&bih=805
@twobob: If you can play a hit song with only six strings on the guitar, you should be able to write award winning code with only five keyboard keys.