Armadillo do magnetic wraps that you might be able to arrange in such a way as to cover the required area? I've used them on my horse's legs and neck to convincingly good effect.
Try FMBS (the ones that advertise the electromagnetic/massage rugs in the back of the Horse & Hound). They have got some magnetic leg wraps with a hole in them for the point of hock to poke out a bit then 3 velcro bits that lock the boot in place! You can still use them on tendons as well. A leaflet comes with them showing the varoius ways you can fit them on different parts of the leg. Hope this helps!
FMB do magnets. I ve just rented a pulsating magnet from them which I strap to his leg and because it radiates out for roughly 12 inches it covers a good area .