Summary

This is a replacement plate holder for the Replicator 2. The standard holder is not very accommodating of plates that are just 1-2 mm different (in width) than the acrylic plate that came with the bot. Also, the standard holder can become "relaxed" over time and won't hold the plate as securely as it should. This plate holder uses a sliding mechanism and springs to securely hold a plate with tolerances of +/- 5mm.

Instructions

I printed both pieces in PLA with 4 total shells, 100% infill, and 0.2 mm layers. The more infill you use, the more rugged and durable the holder will be. There is a lot of stress on the part due to the springs so I do not recommend using less than 50% infill.
For the main body, use supports carefully, or not at all. There are long horizontal 'tunnels' used to hold the rods (mentioned below), and if your slicer wants to fill those with supports then you will be sorry. Supports would be nice, but are not required, for some of the other cavities on the bottom of the holder. When in doubt, don't use supports and you should be fine.
For the slide, you must use supports.
This print can be challenging, but the type of people who need something like this are likely the type that are up for the challenge. It is critical that this print not warp. Needing high infill doesn't help that either. If you normally experience any warping or lifting off of the build plate then you might think twice before printing this.
In addition to the printed pieces, you will need two springs (http://amzn.com/B000LNXYHC). These are the same springs used for the Rep2 Extruder Upgrade (http://www.thingiverse.com/thing:42250), so you might have some already.
You will also need three steel rods, 3mm diameter and 130 mm long. Bevel the ends to make inserting them easier. Two are inserted from the rear, and hold on the slide and springs. One is inserted from the front, and adds to the stiffness of the whole thing. I did not have to glue them in place, as friction was good enough. There are access holes on the bottom to help in removal of the rods if you need to do that, but they only work if your rods are close to 130 mm long. My rods were scrap pieces that I had, so I can't tell you where to get them from.
The three screw holes are intentionally plugged with a thin layer of plastic. This is to provide a bit more area for adhesion to the build platform, and increase the likelihood of a successful print. You will have to clear this out before use.
To install it, first remove the old plate holder by removing the same thumbscrews you use to level the plate. The old holder will simply lift out. Remove the screws and springs, then install them on the new plate holder. Finally, install the new holder back into the bot and re-level.
On the back edge of the holder are some "handles" used to compress the springs while installing the build plate. It takes a good amount of force, and I recommend using both hands to do this. Set the plate approximately into position. Using your thumb and pointer-fingers of both hands, squeeze the handles. Then using your remaining fingers move the plate into position. This sounds difficult, but it isn't that bad once you try it.
This plate holder is designed to hold glass plates that are 3/8th inch s thick. It can also hold the standard Rep2 acrylic plate. Thinner plates can be used, but you might have to print some spacers. There are three holes (8mm dia x 5mm deep) that are intended to hold those spacers, but you are on your own to design them.
Sorry for the bad formatting of these instructions. Thingiverse keeps messing it up.

Rep2 Plate Holder