Probably you wont even need the j-mate... put the wheel as it is, it might shift fine, but you will lose one or two cogs. You need to set the rd limits again, this is sort of critical.
You can buy a campagnolo freehub thingy with a shimano pattern. Swap it, done. Look at the web, i have see them. Smart move from campy anyways.
Thanks...Uman.