I've only done a 12 before, but I seem to remember having to hand the organiser a completed form with details of any supporters, with car reg etc. I guess this is for traceability in case of transgressions etc and I'd imagine (it being a championship event) the same rules would apply here. If you're looking to offer generic help, it might be worth dropping the organisers a line (details via the ESCA 24h website) cos I know they're still looking for people.