I used to get wrist pain. I realized that it was just a little muscle fatigue comeing from my acoustic. The actual agonizing pain came from cracking my wrists afterwards. So, I dont know wether you crack your wrists or not, so, if you do, stop, and if you dont, dont start.
I dunno about Marty Friedman's articles, but I have seen stretching excersises posted in Guitar World by Kirk Hammett.
What you do is hold your hands like Spock from Star Trek (the Live Long and Prosper thingy), then hold your arms out, either in front of or beside you, and point your hand up, perpendicular to your arm, then repeat, only now, with your middle and ring fingers together in the middle, and your pinky and index spread apart from those fingers.
I find they help loosen you up more, like stretching before a race.