Thanks for the reply everyone, some great ideas in there.
With regards to the ADGC, do you think it's likely that I'll need a new nut or will the tension in the string be enough to keep the string in a gap that's wider than it's meant to be? I'm kind of liking this idea because it'll require the least amount of modifications and I cam easily change to something else. Once I de-fret, that's it!
Incidentally, how is defretting likely to sound on a cheap bass? I've replaced one of the pickups with some SDs so it had a reasonable sound, but if it'll be so far off a reasonable fretless sound, it might not be worth it?
With regards to gigging, at the moment I'm a bedroom player between bands so keeping a spare isn't so much of an issue really. It's a very good point to raise though, definitiely one I'd consider if I was gigging with any kind of regularity!