Thanks for the good wishes everyone. It looks like I'll be fit to run on Monday.
I've spent the 10 days doing everything possible to get my ankle working again after my acident and it's about 85% normal now and getting noticably better everyday. The swelling has just about gone and I've survived a couple of 90 min low impact gym sessions.
With another 3 days to go, I'm confident enough that I'll at least make it to the start line. I'm still not 100% certain that I'll finish, but time will tell. It's not exactly been a text book taper into the marathon, but at least all the hard work had been done when I went down so I've only missed a few easy sessions. I'm hoping that, and my sheer pigheadiness will get me around.
As far as gel belts go, I'll probably carry a very cheap Hilly waist belt that I bought for a recent adventure race and put some gels in that. I've also found that if I don't want a belt, then I can poke a couple of gels into the waist band of my tri shorts and they stay put with minimal bother.