I would just try and be polite and honest. Try and tell him you really enjoyed his company, but he is just not someone you can see a future with, and you would rather tell him now than string him along.
Guys actually take rejection well (most, that is!) as long as you are up-front, honest, and polite. They hate rejection when you are rude or be like, "Omg you're a fat loser, as if!"
I wouldn't bring in the "maybe we can be friends" bologna, though, because he might take you up on it, and that's the last thing you want, rejection twice!
He's on a dating site, he'll find others!
Kaida- CT Female 2.5 Gal.
Julep- HMPK Male 2.5 Gal.
Fandango-HM Male 10 Gal.