I did end up ordering some of these Borderlands style Claptrap robots. They are 28mm scale and should fit on a 25mm base with no problem. My intention is to paint them up in my Tau army color scheme and use them as Marker Drone counts as. I think it'll work out pretty well and fit the general theme of the Tau.
Claptrap 3D Design Image
I'll take pictures of them assembled when they show up. The website said they likely won't ship until September 10th or so.