I used to use a 2L Camelback inside the pack. I just let it sit against my back inside the pack. I actually cut an eye-shaped hole in the pack to put the hose through - but you should be able to let the hose come out of the zipper.
You can buy hose clips for pretty cheap that clip on your shoulder straps and hold the hose for you.
_________________________
- deliriousNomad