If your objective is to provide enough of a flat surface for an adhesive strip to hang something, I'd try taking a 120 grit sand paper, scuffing the small region where the plaster is and applying a little spackle with a small putty knife, probably nothing over 3", just wide enough to cover the area where the strip covers. There's a fine art to applying mud or paste and leveling it, so if you're not experienced, you can practice a bit. Spackle comes in small containers and has glue in it, and that should do a pretty good job of adhering to the plaster. If the curvature is minor, you shouldn't have to worry much about shrinkage. You can take a hairdryer on a low setting to expedite the process. Once it's hardened, voila, you should have a level surface with some texture that the entire adhesive strip will bind too. If the plaster has been painted a color other than white, it will be unsightly, but if the goal is to suspend a frame, the frame should conceal it. When you move out, it wouldn't be anything to take some 15-minute dry mud and conceal and sand the whole thing down and match the paint, so you're not really damaging the wall in any manner. The only other choice that comes to mind is using a concrete screw like a tapcon or something more extreme like an expansion-type anchor bolt, and both techniques involve using a masonry bit and boring into the brick.