looked at doing somethign similar with the RX8
As later models had a flick key. where as the earlier ones had a normal key and crap fob.
but because the key has the imobiliser in it, we were looking at circa £150 for the key and reprogramming. Though it was ebatable whether it could actually be done.
So I dont think anyone in the OC bothered in the end.
A flip key for the Z is doable. There are a few guys on my350 that have done it.