starkad said:
Now I'm a little more on his side of things. Obviously, he has a great deal of difficulty selecting one possibility out of billions, and when he forces himself to do so, it rings false. For whatever reason that might be one of his limitations. It might make the situation untennable. But I don't think so.
Maybe as least with DnD he just needs that seed to get the process started. So you could DM him in a solo adventure or two, then he could extrapolate the character to the appropriate level from there.
But you're still not really talking to him. Perhaps that both of your faults. "I don't know about spycraft, don't count on me." Doesn't translate to, "Bow to my will, serf! Now, kiss my ring." Make your pitch for spycraft as a change from the now all too familiar fantasy. Listen to him, if you're unsure about what he's saying, it's probably a good time to ask for clarification. Sometimes, good friends have different tastes.
One time not so long ago, I thought I was introducing a friend of mine to the sublime pleasure of the highly entertaining Super Troopers. He saw it a little differently. He was certain I was trying to torture him, possibly to death. His response was to make me watch The Mummy Returns, for which he later appologized. Between good friends even that can sometimes be forgiven.
But let's be honest. You are trying to force him to do something he doesn't think he can do well. And he's trying to force you to suffer something you'd rather not. Of the two it certainly seems you're being the least reasonable, perhaps because we haven't heard his position yet. He doesn't have the "imagination" to write a compeling, and significant backstory. Your solution is, it's simple, just use imagination. How does that even address his supposed problem?
That said, the Frodo Baggins suggestion isn't a bad one, you might need a house rule to make experience reasonable. But it could certainly lend an important dramatic element(s). You seemed to dismiss it without consideration. Your choice, of course, it's your game after all. But it certainly casts suspicions.