Waist Band is now too Large

I have an Osprey Kestrel 28(?) in small. The waist band itself is not adjustable, but I have found that it is not tight enough around my hip to provide the kidn of support and weight distribution that I need. I am leaving for Kilimanjaro in two and a half weeks and am wondering what I could do about this?

I am considering cutting out closed-cell foam and sewing it in with mesh to line the hip belt to add more cushion and take up more space (basically to give me more inches). Any thoughts/suggestions?

Or, you could take it to a professional tailor who could problem solve that for you. You will also probably lose a little weight on the trip, so adding a belt may not be a bad idea either.

Have a wonderful trip!

Does Osprey make a smaller belt? You could check with them.

Well, the waitband is not adjustable at all to replace this one...I suppose I could ask though just in case they have suggestions as well. Also, I did take it to a tailor (a shoe repair as I figured they may have the heaviest-duty threading and also a regular tailor) but there was nothing they could do in the way of decreasing the waist strap and we were limited in "bulking" up the padding..
I was given the suggestion of closed-cell foam for the extra "bulk" though if I wanted to bring that in. I made-shift with this and a doubly-lined mesh cover and it seems to be helping tremendously. I might take this into the tailor to have them professionally fix it. Thanks for the suggestions!