I did what David Olsen suggested with a dark green 'white widow' spectra gridstop pack made in 2007. The fabric is similar in weight, around 4 oz. For strength, a light half inch webbing was used rather than grosgrain or twill tape for the loops.
The sleeve does not go completely over the pack contents, leaving an opening of a few inches when tightly cinched at the top. But this is OK, because there is another sleeve sewn inside it made of lighter WP fabric that has lighter loops of quarter inch wide cord with another drawstring and cord lock. The inside sleeve cinches up to a tight closure (there is a top pocket that goes over this).
The idea was for the outside sleeve to take all the pressure of compressing the pack contents, and the inner sleeve to provide water resistance. It has worked very well, with no loops pulling out. I don't think grommets could have withstood the pressure I put on the outside sleeve when jamming everything in for a week.
Sorry I don't have a photo of the pack with the top pocket off and the sleeves in view. The dark green gridstop makes it hard to see any detail anyway. Here, you can see what I mean:
In addition to the top pocket and tailored bottle pockets on the outside, there is an additional envelope pocket on the inside for maps, notebooks, flat items that need to be kept dry.