All right. I'm not very familiar with the illusion x tower, just from what I've seen in pictures, but I do have a few ideas. If you take this concept from this watch / picture you could use the "face" of the watch as a surface to weld a holder onto. Of course this would have to be a custom sort of band that would wrap around the awkward shape of the illusion tower.
Next idea would be to use a plunger. I know you don't want a suction cup type of setup, but a plunger (painted black for looks) would suction on fairly tight to your tower. You could also reinforce it's connection by securing it with zip ties after the plunger has been suctioned down to the tower.
Just a few ideas I had at one in the morning.