I started digging into the issue of reducing the alcohol in tinctures, and the information is not promising. First of all, heating up the tincture will change the properties of the plant material - remember, in most cases, during the tincture making process, the herbs and alcohol are never heated.
Once heat is administered, it can change the properties of the herb - for example, let's take Avena sativa - a tincture I make at home and have used for many years, and have experimented a bit with. If I take it in cold water, it has a more of an extended release to it - but take it in hot water and the effects are usually felt immediately. For avena sativa, it's harmless to do this, but we also are not talking about
adding it to boiling water, as that would lower it's effectiveness.
The alcohol is part of what extract certain plant constituents (water extracts different constituents), and by boiling off the alcohol, you will change the tincture and what it does in some instances, because you will be (if nothing else) boiling off some of the water extracted constituents - but very little, if any, of the alcohol will be affected.
To support this, here are two sites I've found, so you can determine for yourselves:
www.camillefreeman.com/2011/12/alcohol/www.ochef.com/165.htmIf a person truly wishes to avoid the alcohol, the only choice is to use glycerite tinctures, where no alcohol is used.