When you say non-permanent, do you mean that you want to be able to get whatever it is off
the trap, or off the wall? Or would you be happy for both trap and wall to have stuff
stuck on them provided the trap could be taken down?
I think your best bet is
something like clear silicone sealant which should quite easily peel off at a later stage
without taking half the wall, or half the trap with it like glue does. But of course it
really depends what the surface of the wall/ceiling is like. It might get damaged if
that's a concern. Also, whether the trap will stay put depends on what sort of contact it
can make with the surface concerned. Ultimately something is going to have to stick to
something else. I suppose you could glue the traps onto a thin sheet of MDF or perspex or
something which you then attach to the wall or ceiling with hooks.