well there is one more option you could use, although its not great:
give it a name that starts with a . so that it is invisible. it will disappear from column view as well, but you can still access it. you could at it to your dock, so you would have instant access.
its probably not the solution that you are looking for, but that s it. either finder shows you mounted volumes, or it doesnt. finder doesn t really choose which files or volumes will show up on a one to one basis, and even if it did, i suspect that any way you could change its attributes for the desktop, would also apply to finder windows in column view.
they are both in finder, after all.