Motivating a Jr. High kid

My son is entering 8th grade this year. He's always been an uneven student,
shining in some favorite subjects (won the school's geography bee one year!),
and sliding by in subjects he doesn't like so much. His teacher, and folks who
are around him day to day, say he's fairly bright. Where I see him falling down
academically is mostly in one thing - he just doesn't like rigor. Memorization,
or anything that needs a lot of careful steps. He can *do* it, and has no
problem with complex things in his model building. But when it comes to
studying, as I've noticed from trying to help him with memorization tasks like
German vocabulary, he loses patience with things that don't come to him quickly.

It was very interesting to me that his self-evaluation, as he spontaneously told
me last year, is just below the cadre of the brightest students. Some of the
other kids come to him for help in things he loves, like social studies. His
teachers pretty much concur. But his impatience with rigor is getting in the
way of even things he likes now, like German and band. He hates to memorize the
vocabulary, he hates to practice. And he's gotten no particular recognition in
school, and was clearly bummed the end of last year when some of his friends did
and he didn't at the awards assembly at school.

I'd like to stretch him a bit and put the 8th grade honor roll as a goal for
him. We've been talking about a PS3 a while after it comes out (I wait for the
prices to drop), and have told him I expect to see him on the honor roll before
he gets that. (He likes video games but hasn't been the type to get subsumed by
them or spend too much time on them.)

I think it's an appropriate goal. He knows high school grades are important for
college admission, and he consistently expresses college as a goal. I've told
him 8th grade marks will be an indication of how he does in high school.

I must admit to being a little at a loss as to how to really motivate him or get
him past this thing against memorization or rigor. I was a kid that had no
problem with these things, although I had other problems like with
procrastination. The only way I know to deal with rigor is just to do it.

So, what do I do with this kid?

TIA,
Banty