At church we have three projectors (two at the front, one shining on the back wall as a sort of teleprompter). Since they are all Sanyo projectors, our head technician set up a system that allows us to control them all from the media booth.
Step 1: Making the Remote Wired
Since the projectors all use the same remote, it was just a matter of opening one of them and soldering a small headphone jack to where one of the infrared LEDs connects to the circuit board.
Step 2: Infrared LEDs to Control Each Projector
There are wires that run from the media booth to each of the projectors. At the media booth end of the wire there is a headphone plug for connecting to the remote, at the other end of each there is an infrared LED mounted behind the projector such that it shines on the remote receiver.
Since these are mounted very high up on the ceiling, I don't have photos.
Step 3: The "projector Selector" Switch
Originally the plan was to connect each wire to the remote when that projector needed to be turned on or off, but to take it to the next level the technician built a little switch box. Basically it's a five position switch that connects the contacts from the remote input to the wires that go to the projector(s) at the:
2. left front
3. right front
4. front (both)
5. front and back (all)