@Adrian, just what I was going to suggest as well, lekos can be great for that scenario. - they're punchy enough and the leaves give you such precision control over the beam the leko could be on the ground and moved around as needed to be out of frame/hit the actor being filmed. If the ceiling is white too you may not even need a show card, though that may give you more punch if that's what you want. One thing to keep in mind is spill from lekos can get messy, be prepared to throw up some bottomers/siders and maybe even hang duvy skirts from the celing if need be as the tops of the walls can get pretty bright if the ceiling reflection is too close. Depending on the lens you choose you can go pretty punchy with a very narrow barrel or just get overall ambience with say a 90 degree barrel.
On the other hand a light with more spread just stuck in the corner somewhere and bounced into the ceiling would fill the whole room and mostly give you a big ambient boost.
Depending on how low the ceilings actually are and if you can get permission to do so there's always drilling a baby/junior plate into the wall if you can find a stud and hanging something low profile - make sure to safety cable it and also drill that into the stud as well. Or if you have the room you could also try a menace arm with a low profile fixture on it, although those can turn into cumbersome beasts in no time when you're in tight spaces.
Don't really know what kind of light you're trying to get up there and how much room you have for it, but another thought is stapling a run of zip stinger all the way up to the ceiling and simply hanging a practical, maybe with a china ball attached. Or you could tape up bare kino tubes, maybe with a cut of diff taped around them as well. Without specifics on dimensions, what kind of surface you're dealing with, how low you can go with the light and what tip of light you'd like up there and how labor-intensive you're willing to get to place it it's tough to say what might work best but there's a handful of options to consider.