I vaguely remember reading about the Young Jack comic when I first discovered the books earlier this year. I'll have to check that out. I like to picture Jack in my own way as well, particularly nondescript (is that an oxymoron?).
He's the type of dude you pass in the Mall, Supermarket, etc., everyday and hardly notice. No bulging muscles, no pretty-boy features. But I would be open to seeing how a really good illustrator envisions him in a Graphic Novel, as long as he doesn't stray too far from what's been established in the books.
That's one of the things that worries me about a RJ film; I just know Hollywood is going to try to pump Jack up so he resembles a cross between Stallone and Brad Pitt. I'd rather not even see a film adaptation if the Producers are going to ignore what FPW has already clearly established.