This isn't really a custom, it's more like an abandoned feature. Let me say first I can't take credit for this. Unreality from Rebelscum discovered this feature, I'm just passing along the info.
Tamer if your reading this, I'm sure you'll love this one.
Anyway, if you notice on all Action Fleet AT-ATs, there are 2 wheels located on both sides, underneath. (Note the arrow)
Here's a closer look. Also, note the tiny hole as well.
On that second pic, you see 2 screws. I unscrewed them, and revealed this. (You can clearly see the wheel part now)
If you take the wheel out, you can see the tiny hole.
I took a string and tied it to the wheel. Then I put the other end through the tiny hole, and attached it to a Luke figure, and here's the result.
Empire Strikes Back anyone?