In the spirit of my usual sublety,
New missus?
I had a look at a couple pics of ZRX's, the rear peg brackets also support the exhaust, and are nothing but cast alloy, so if youve got aftermarket can(s) as well, forget it, no amount of lengthening or rubber washers behind the mounting bolts is gonna fix it.
Best bet, find out if anyone makes an aftermarket peg with a rubber pad on it, or see if you can retrofit the rear pegs off a bike that has them, the Ninja 1000 has a rear peg thats almost identical to the riders with a big fat rubber foot pad bolted to the top of it, changing a footpeg is literally 1 circlip, and takes no longer than 4 minutes (had to change the front after my driveway drop and theyre a lot more annoying due to springs etc)