I exercise, but I haven't quite been able to become as obsessive about it as fully as I can about other things.

How about you?

I think that the idea of directing our intense focus toward constructive things is good, but it might take some effort (and perhaps some good techniques) to learn to direct our obsessiveness to a particular activity. Obsessions have a way of emerging without our choosing.

Has anyone else tried redirecting?

What I use as exercise is simply muscle contractions. It's also called self resistance exercise or dynamic strength. I use my mind to effect contractions in which I use any or all muscle groups and fire these up until I get the desired level of pain/pleasure I am after. Growing muscles, strength and fitness are the byproduct lol!
Since making the connection or re-direction as you say, it's an automatic process I can pursue in every position and every situation. And my body feels stronger every day as a result. When I tell an NT, they can copy the process but afterwards they are not able to remember to do it.

I believe it could actually be called stimming, apparently a common Aspie thing. Anybody have any stims to share?

I struggle with the exercise thing as well for part of the same reason. I also have had many times where I'm all "I obsess over the stupidest shit, why can't I obsess over the important things?" I do try redirecting sometimes, but I get re-re-directed to something else lol. Sooooo weird. It's like the negative block on things just puts itself up no matter what. If you can afford it, try the Wii Fit and EA Active game. I've been on it consistently for about 2 weeks and it is helping me. Only about 30 minutes at a time, in my own living room, and the exercises vary enough to not have me bored. So far so good...until i get distracted again lol. Hope this helps!