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Well, it looks easy yanking a stump out of that... that potting soil there. I'll bet it would have been a real challenge in heavy clay.
Back to the original idea, maybe attach the root cutter device on the FEL. Hook it into the soil, back the tractor up, and cut most of the roots. I think you could get more power into the root cutter by pulling it with the tractor than with a small hoe. Once a few roots are cut, the hoe with regular bucket could finish it off pretty easily, and no tool changing necessary.