Easiest thing to do,
Assuming the guys that are doing this arnt using the rear wiper (Doesnt matter if you are but you will need to run wires from a switch and position of solenoid might change)
1) Get a central locking motor from a kit (Can be picked up on ebay or do a wanted ad) + the fixings
2) Mount the solenoid as shown in the picture, you will need a little connector box thing that connects the two metal rods (Before i found one i was going to use a chocolate box (Used for attaching wires together, avaliable from any car shop)
3) I used an original hole in the boot and a self tapper easy
3) Bend the rod from the central locking kit so that it linesup next to the original boot rod as shown in the pic, this can be done with a vice and plyers, you should be able to do it without the vice
4) Once its all mounted simply cut the plug from your rear wiper to leave 3 wires, connect 2 of them to the wires of your solenoid, everytime you press the rear wiper stalk your boot will pop
5) Replace the rear wiper relay with a headlight relay, this will ensure it only pops when you press it, and not every 10 seconds like the rear wiper
6) If its wired up to the rear wiper it only works when the key is in the ignition which is good for security!!
(Its also easy to pull new wires through the boot, just tape a screw to some string and drop it down from the top, tape the wires to the string and pull it all thru)