I own a CTAC. I think the main problem you will encounter is that the holster will lose some stability if worn OWB. The design of the holster provides for your pants and belt to secure the whole rig in place. The belt clips are made to hook over your pants, then have the belt run through the outside of the clip. If you eliminate the clips going over the pants, you decrease stability. And I'm not sure the system will be reliable or all that concealable if used this way. If you don't have a CTAC, I wouldn't recommend buying one just to try it out. Maybe you could find a buddy that has one and experiment - you may be able to make it work.
If all else fails - spend another $40 and buy a couple pairs of pants that fit both you and your holster. +1 to Jim.
I would also like to add that the CTAC is an awesome rig. I was very skeptical of it at first, believing it would be uncomfortable. Boy was I wrong. Even with the Kydex (I was nervous about the Kydex digging in), this holster system is much more comfortable to carry than the many cheap 'tuckable' style nylon holsters with a single clip sewn onto the front of them. With the CTAC, the weight of the weapon is distributed over a large area across the waistline and after an hour of wear, it's easy to forget it is there. The holster can be 'canted' in many different variations to suit your body size and type. The holster and gun will completely disappear under a loose shirt, even a t-shirt - I carry this way regularly. I have never tried going formally tucked, but the rig is supposed to work that way as well. Hands down, this is the best $70 I ever spent on a holster.
Good luck.