Pete, Find a compromise position for the mic between voice and guitar, apporximately half way between, maybe six inches higher, at most. Turn up the gain on the mic as much as the room will stand without feeding back. Make sure the main speakers are positioned well away from the mic. Stand back from the mic about a foot to 18 inches, not more than two feet away, and pick and sing in a normal fashion. It may work if you have a fairly decent mic. If you have real junk, nothing will help. And if this advice has already been given in a previous post, my apologies. I read your initial post, & just started writing.
Jim