He will take any form of rejection, no matter how nice you are about it, badly.
Don't offer friendship, he will be gutted.... it's like the final insult.
Just tell him you dont want a relationship with him, and don't spin out the story too much.
Then show your friendship, by being friendly towards him, but not leading him on... if you understand what I'm saying.
Good luck.
PS.
find teenage 'speak' so refreshing.... so he has a crush on your fancies or your whatever? Bless him.