Unfortunately, there is no ring system for this lens, at least for my housing (Sea & Sea). Thus, I tried several alternatives to use the zoom of this lens underwater.
My first test was using some kind of foam tape around the zoom in the lens and then put my S&S 60mm focus ring system on top. This seemed to work since the Tokina lens is only slightly thinner than the Canon EF-S 60. This system not only looked bad but also was not very stable. The zoom ring would tend to get out of the place and eventually fall out of the lens to the Dome port - Not such a good idea.
For my second test I used elastic bands (the ones you get for adjusting your clothes) and put it around the zoom. This seemed to work pretty well at the beginning - looks good and it is easily removable from the lens. For this one, I had the help of Rita, my mother-in-law, who generoulsy offered herself to teach me in the art of using an electric sewing machine (cool stuff, let me tell you guys!!!). The problem was that the zoom ring would still tend to fall out of the lens. The problem is that the o-ring inside the zoom ring is in the front of the ring and therefore it would not touch the elastic band.
Third test - final solution: I bought some velcro tape and "glued" it inside the zoom ring (in the oposite side of the existing o-rings). This mad the velcro tape "grab" the elastic band and the zoom ring feels now snug in the lens. I tried already several times and it works perfectly. Just be carefully to check whether the AF is still chosen since the elastic band might put it in MF when putting the zoom ring in the lens.
Since I glued the velcro tape in the lens I still had to make it work with the EF-S 60 lens when using this. For that, I slightly cut the velcro teeth so that they would not scratch in the 60mm lens.
Some pictures below of my solution: