You can get a slim ballast kit from Acumen for just under �100 - http://www.acumen-electronics.co.uk/..._Ballast_61014

The ballasts are supposed to be sealed with a suitable IP rating to allow them to be mounted anywhere on the bike.

Most of the situations I've heard of where folk have fitted them to bikes, the increase in light produces by them has rendered full beam fairly useless so I'd stick with the dipped beam only.

Al.