This product was mentioned in
with an average of
Ah okay, think I kinda getcha now. Yeah a harness akin to a shoulder holster should be able to offer some support. Far as that goes, so would some suspenders under the rest of the attire with a back strap for increased tension.
Run a strap (maybe two if given the weight) up your arm to attach to the strap going over your shoulder and I'd think that'd do you fine.
EDIT: Dunno if you can fit it under your clothes, but maybe something like this also? [link]