On VERY low heat, your THC is safe. Even something like putting it in a glass lasagne pan and the placing the pan on one of those back-pain heat wrap things would help evap off what you don't want. But then go too far, and you end up with goo-hash rather than a tincture... Also the alcohol evaps off first, and your resins are not soluble in water.
Do you own a potato ricer? That is great for pressing out every last drop of goodness from the spent plant matter.

REad up on 'Green Dragon' if you haven't yet. I've used Bacardi151 with as much weed as I can stuff in a jar, a few mint leaves for flavor, and leave in a nice warm place (atop the fridge) for a week. Drain, strain, squeeze, enjoy.