Microvox are worth a try. They make mics that attach to instruments using velcro so they don't pick up body vibration. (also so you can remove them easily, which may or may not be a concern for you).

Though HG's are mot specifically mentioned on the Microvox site, it is well worth dropping Alan an email and asking him. He's always very willing to help.

Whatever happens, you will need to experiment with placement. HGs are all different and there can be no simple rule.

Anahata