Most bindings have an adjustable heel piece that can slide forwards and backwards to accommodate more then one boot size. Have you checked the range of your current bindings heel piece track to see if there is any chance of them fitting your boot?
Also, if this is the third remount, you need to consider the current set of holes in the ski plus the previous set of holes. The new mount (the third one) will have to be placed so none of the previous holes are affecting it. This can make picking a spot to mount semi difficult as your options can be limited by the previous mounts holes and their pattern.
My suggestion: When you take them to the shop, see if the tech is busy and if they aren't see if they can do your stuff right away (be nice!). That way when they pull the bindings off they can show you whats up and where you can remount (again, be nice!)