I did mine a few years ago with the proper white tyre paint. It actually looked quite good but cracked as soon as a rode the bike! Very difficult to make a neat job of it as well.
I did it on my R6 a couple of years ago. You can buy a white "TyrePaint" pen from most car/bike shops (Halfrauds too). Takes a while, do it carefully and make sure the tyre surface is very clean and dry. The paint never cracked for me.
This is something I can still not decide whether it looks cool or tacky. Jury's out I reckon......