Well I've got several of those white nylon wheels at home (or at least used to) so that may not be a bad shout... They seem a little brittle from what I remember though; I'd have thought they might crack if you put screws in them...

Now there's the problem that I don't know if I still already have a set of white nylon wheels, and I wouldn't have time to buy them if I get home and not. Plus, though they're only 80p each, they have £5 shipping on them, so I don't want to buy a pair to find I have loads at home... I'll have to give my dad another thing to search for!