initially, this is what i'm thinking without making it totally crazy.
just relocating some of the fringe/outlying keys to make a tighter matrix
and wiring like this
this isn't final, just my thoughts. take a look, see if it makes sense & let me know.
also, please include the controller you are planning to use. i know i suggested the teensy ++2.0 but not sure what you went with. (will be a determining factor of how the matrix is laid out).