So yeah, a belt - with a diaper.
Ive never seen anyone mention it or say that they did, but I allways do, I put the diaper on, and typicly i wear bambinos which have a fairly high rise, then I put a belt over it jus at the point that it covers the top tapes, tighten it jus as tight as i can and then fold the top of the diaper down over the belt.
I got the idea when i had some abri-wings diapers - they have a built in belt type deal and the front jus velcros on, but using a belt with bambinos is great. It keeps them up high and tight.
So if you got a belt handy, and it needs to be a rather thin one, give it a try and report back what u think.