ya im a bit confused my self, having a common ground is actually a very desirable thing.
if you ran a seperate ground for each button you'd have twice as many wires in the cab.. at least with a common ground you can just piggy back them from button to button..
if you really wanted to with a ground to each button then it could be done easily.. although i do not know why anyone would want to as it's more work.
get some terminal blocks..
then run the ground to said blocks.. (only need 1 wire going to the terminal block)
then for the rest of the terminal positions just run a jumper wire dasy chain style.
you would end up with a whole block of nothing but ground connections.. then on the other side of the block just attach the wires to go to the buttons..
another way to do it would be to get a bus bar, you could even make your own with a strip of sheet metal, attach it to some wood.. , then run the ground from the ipac to it..
then for outgoing ground to the buttons.. just pick a spot on the sheet metal and put a screw though it.. voila you got a as many ground wires as you want limited only by the size of the piece of sheet metal you use.
again.. dont know why you'ed do this as it's more work but there ya go.