I know this is an old post but I searched it and here's what happened. I had the same problem with my Nikon 70-200 2.8. I notice that when I shoot this lens I tend to roll my zoom with my left hands middle finger. So I need it to grip.
This morning I brought it to work and fixed it. The DIY fix process was; I flipped the rubber grip that was completely loose inside out. I never removed the grip from the lens, I just turned it over to the barrel closer to the front of the lens. Next, I used painters tape and construction paper to tape off the areas on either side of the inside out grip (note: I did one end and slid the grip down a little over the tape and then taped off the other side. This way I could slide the grip over each taped end a bit before the next step). Next, I used a fairly aggressive spray adhesive (Its a 3M called '77') and evenly sprayed one light coat onto the backside [inside out side] of the grip. Next, Remove all the tape and flip the grip right side out onto the lens barrel where it belonged. I ended up 'working' the grip back into place with my fingers for the next couple minuted to get it lined up. The last thing I did (USE CAUTION) was to take a heat gun and gently warm up the grip (mine had loosened because it was streched as well. The heat shrank it a little to fit better). ONLY do the heat gun thing if you are sure you can handle it. In my profession or 'day job', I build sets and scenery that you see on tv (like the sit-coms and news sutdios) so I work with these kinds of things all the time. So be careful and this should only take 10 entire minutes and save you service cost plus down time!
Hope this helps!