It's a roll of double sided sticky foam type stuff (fairly thin).
Cut a square for each corner of the number and hey presto. It sticks fine to both the number and to technical fabrics, and it's never come unstuck for me in the rain or wind. Indeed it withstood 4hrs and 19 minutes of torrential rain and gain force winds in the Greater Manchester Marathon earlier this year
I've got shingles at the moment too - I can sympathise! Leading up to the rash I was feeling pretty rubbish for a week or so and not really feeling like running anyway, and still don't to a certain extent.
Mine is still too painful to really be running, but part of that is because the rash goes over my shoulder and front of chest which is right where my bra stap would be - but judging by your name you won't have that specific issue!
I can't quite work out if my rash is actually painful, or whether it's so itchy and prickly that it feels painful too.
Being that it's caused by a virus I'd probably say that running isn't a great idea whilst your body is trying to fight it off, and when you do feel better the advice seems to be to return to everything gradually and slowly - sometimes easier said than done, but I think it's easy to think that once the rash has cleared up then that's it, which may not necessarily be the case.
I didn't do it last year (the first one) but a bit of research tells me that it's practically pancake flat - and whilst it starts and finishes in the town centre it seems to take in a fair bit that's not to 'towny' if your wife isn't keen on that. It looks like it heads out to Cookham, Bray etc and includes a stretch along the Thames. There was around 1700 finishers last year I think.
A Google search found the following link, which should give you a bit more of an idea, especially if you select the satellite view on the map.