Well, I kind of pity the guy. My guess is that he's a socially awkward person, and you've been sending him conflicting signals. I'm sure if you weren't acting nice to him in front of his face, he wouldn't keep trying to call you. If you suddenly drop a bombshell like "Yeah, that's great, but I wanted to ask you, what do you want out of talking to me?..." I think it could seriously inflict some damage. He would lose trust in later relationships, or just be too scared to approach anyone any more. What you have to do is to break down the signals so that he becomes to realise what the situation is himself. For example, keep ignoring his calls, avoiding contact whatever, and if he brings it up, then say that you don't really connect, and that you can't give him what he wants etcetc.

If he was being incredibly unreasonable and stalkerish, only then would I recommend straight out rejection as a last resort, but as it stands, I think you should take some responsibility for giving him some hope in the first place.