Get a good Key Grip and look for the solutions. There is always a way to put up a rig, depending on what you want to achieve and your budget\ingenuity. C-Clamps with cribbing, Pole-cats and wall spreaders are amazing. Clamping above drop-down false ceilings are options, or maybe scissor clips if it's a false ceiling grid. I've been able to talk some locations into letting us drill baby plates into the ceiling, but some places won't allow it - for good reason! Even on low-budget shows, I've been really impressed with our ability to hide hanging lights and make them work. My gaffer would recommend getting some Socapex to keep the cabling manageable -- we got bit by this recently, and it was a mess that cost some time to move. We just didn't have the right stuff.
If there are recessed light sockets, you can get these handy grip items from Modern Grip Equipment ($30 each) that are made of plastic and have a baby spud on one side and a medium screw-in base on the other. These will screw in where the light bulb is and put a baby spud for your light. Molded plastic or PVC so they don't conduct electricity. Then buy a small pig nose at the hardware store, and you can get both a spud and a little power for a small light (I don't recommend more than 300watts or so because of the small wires inside).
Also, I've had the idea to put up a truss grid supported from the ground, if you can hide the legs with art department (columns or dressing). This is a little more intense and expensive. And the other idea I've used is to tape white showcard to the ceiling and bounce a Source 4 or a Tweenie on a pancake into it. This will at least bring up your ambience, though it's not necessarily pretty.
An opposite problem I had was in a location with white ceilings and light hardwood floors, and I wanted to cut the ambience down. I wasn't allowed to hang any lights or attach anything to the structure. The production never used the location, in the end, but I had the idea to fill garbage bags or visqueen with helium to put black on the ceiling and knock down the bounce. Admittedly, I've read this idea in American Cinematographer once, but can't remember the exact details of material and so forth, so if anyone remembers this or has experience with it, let me know.
-Graham