I think I would just use a smaller diameter water bottle unless there is a particular reason you need a nalgene. Those bottles are quite heavy. You might look at reusing a pop bottle or aquafina bottle. Sometimes I use a lightweight bike bottle as I can use it one handed (no unscrewing a lid) and they are very tough. I use that for my easy access water and if I will be going longer distances without water I can fill my platy that I use for in camp.

You might go ahead and post a pic or link to your pack as there are some very innovative people on here that can help with ideas. Good luck.

-Skippy