REG had sent me a replacement set of pickguards for the EDS. I have yet to receive a pickguard from REG that isn't warped in one way or another. The lower one was fine, in that the warps were in the right direction and it laid flat when screwed to the guitar. But the middle pickguard (now using the Page 6-screw pattern) wasn't going to lay flat. Since I currently had a decent pickguard on the guitar, and was just considering replacing it for the "Page look" - I figured I had nothing to loose.
So - to fix it:
Heat your oven to about 180 degrees Fahrenheit (or about 82 Celsius for you non-American folk.)
Lay the pickguard on a flat surface. If you use a baking tin, than some aluminum foil under it is probably a good idea. I had some thick tempered glass that I used.
Place the pickguard in the oven and heat it for 10 minutes. This will be enough time for the pickguard to become soft, but not too soft so that it loses shape.
Remove the pickguard form the oven and press it flat. Some people will put it on a flat surface and put heavy books on top of it. I had 2 of these thick glass plates, so I sandwiched the pickguard between them and then clamped them together.
Then set the pickguard aside and let it cool for several hours (even overnight isn't a bad idea.) In my case, I didn't have patience, so I removed it form the plates about 8 hours later. It had cooled and stayed nice and flat.
Don't heat the oven over 180, and don't leave it in too long - or you can risk damaging the guard.
The two most important things to remember in life: "The only time it's acceptable to work with amateurs is if you are making porn." "If you want to work with clowns, join a circus."