Default Change M7 carkit into M8 carkit?

Last year I bought a HTC One (M7) and bought a carkit with it.

The carkit wasn't exactly cheap, around € 50. The carkit for the M8 is almost the same, only the plastic holder is a bit different. But this is probably a piece of plastic that costs a few cents to make and a few euro's to buy.

Anyone knows if this is possible to order only the plastic holder somewhere? Because I don't like buying a new carkit for just the plastic holder.