Kevin, assuming that you do not drink really cheap stuff, there should not be acetaldehyde in the alcohol you drink. Acetaldehyde is generated by alcohol dehydrogenase (an enzyme), inside cells.
There are several forms of this enzyme and it is in the liver, stomach and at least for baboons (hey that is what I came across) in virtually every tissue including esophagus (and brain and heart). Without checking on this, I presume that also includes human oral tissues. (How else would you get the chemical there).
So this then indicates that it is in the oral tissues where acetaldehyde is generated and for that you need to have alcohol present whether that is a mouthwash or a 20 year old whiskey. BTW how on earth do you tolerate 50% proof mouthwash???!! By that logic using a Peg tube you would at least not endanger the oral cavity. Although there would be little point of either mouthwash or a 20 year old Whiskey via a PEG. It is also thought that alcohol facilitates the entry of carcinogenic tobacco substances into oral tissues.

I would stay away from the mouthwash, use Biotene instead.

However, please realize that the human body itself produces alcohol! This is not an endorsement for drinking!

Markus