When I had retail shops we also had a similar problem. In the end we chose the ones we would support, the local hockey club, the pony club and several others. Put them up on the wall in a frame as being "Officially supported by the team at XXX Electronics".
Some of the staff had an interest in some that we supported so that worked out OK as well.
When people came knocking the receptionist simply pointed to the frame and said "sorry, they are our officially supported causes - no room for more just now".
