Painters use special duct tape for hanging plastic on brick and stucco. Sherwin-Williams has it. It is super sticky. That would probably work. A double-sided foam mounting tape might be an option as well. Bud has a good idea though. Make a couple of little holes in the mortar and anchor a piece of wood on. When you want to remove it, filling a few little holes with mortar is easier than trying to scrape off a sticky adhesive residue that has been on there for 10 years.