Okay, i dont see the point in doing this because its not like thay effect you or anything but, theres only one way to to it, and thats to, make a new account on your ps3, remember you can name multiple accounts with the same name, then just go to the game data utillity, Press triangle and copy them to your new account, you will then have no trophies on the 2nd account, but will still have all of your save data, and if your worried about your online gameplay dont worry, just go to Sign Up for a playstation network iD, and click use an existing account. You will loose trophies for all games btw, and im sorry to say there is no other way.
P.s To all users, i've just signed up for this forum, and i didnt look to see if the topic was dead, so sorry if i have majourly bumped this.