I had the same problem and tried to relax. I even resorted to Zen meditations and nothing worked. I recommend just buying the modified controller. Yes it is gonna cost about 50 bucks but it good because
1) the controller cost 30 bucks so the parts and labor actually cost around 20 bucks. Sure you can do the modification yourself if you have half a brain but if you should screw up in anyway, now you're out a controller.
2) you will NEVER have the accidental presses anymore. After smashing a second controller in just under a week, I decided the modified controller would actually be an investment! I also got one of the first ones made and it ran me like 70 bucks.
3) if you play the game often, do you really want to get mad in every other firefight? The game has plenty of issues to cause us unneeded heartache all the time. Why not fix a problem yourself if given the opportunity.
Just my opinion
Here's a link to a site thats been around for awhile.
http://www.socomcontrol.com/