Personally I'd skip the dorm and live off campus in a nearby apartment with less rules but if you prefer dorm living or are forced to here's what I'd do to hide the ballast.
Make sure to fully enclose all the gear you need to run it and it'll probably look neat enough to pass inspection. Open ballasts with wires, ballasts mounted on wood, and the like won't pass inspection.
I usually use
small aluminum enclosures for my ballasts. If you mount them securely, use the proper cord grips, and use rubber feet it'll look neat enough. If the ballast tends to run hot, give the thermals a check too. I usually check ballast temperature after 2 hours of operation. On some of my more hot running ballasts, I ended up cutting ventilation slots in the case. Finally put a line fuse on the ballast input, I usually size them at around 120% of the ballast name plate current draw.
Finally give the case a coat of black paint and to the average person, it'll just look like a slightly larger power brick.
A lot of dorms also prohibit halogen torchieres so I'd avoid using any fixture that resembles those just to avoid extra scrutiny. Also if you know when dorm inspection is to prepare, hide any sketchy looking items out of plain view, a closet will do as RAs don't typically go searching through your stuff but your car if you have one also works. Another good way to avoid extra scrutiny is to keep your living space tidy and clean on inspection day, no excessive clutter, bathroom clean, floors swept, bed made etc. The RA will probably just do a sweep of the room and move to the next one.