I don't use a hydration bladder, most of my backpacking being done where I need to carry a liter at the very most, and usually only half a liter. Although this summer on the drought-striken west coast may be a bit different!

I know that ULA has removable hydration bladder holders, because if I got one that would be the first thing I would remove. Both ULA and (especially) Elemental Horizons will do custom alterations, so phone calls to them will elicit a lot more info than their websites! They could tell you what would work with your brand of bladders or provide alterations to fit.

With EH, I would also suggest the Kalais rather than the Aquilo, which is a really large pack!

Since the CDT is frameless, I wouldn't suggest that unless your wife's total pack weight will be 15 lbs. or less. I was thinking of getting one for me as a winter day pack.