a little more serious answer, or at least helpful.
as you say, if with the gloves you already have, the issue is at the seams, I would think you would have some success with seam sealers, although unlike a tent, the seams in a glove have to deal with the finger curling/bending, so it might be hard to get a long lasting solution, just because the sealer is getting moved a lot, and the seams can be pulled here and there a lot.

while I was goofing around with my answer before, thin wool or polypro inner gloves can go a long way with helping with greatly reducing the "clamminess" feeling that will invariably happen.

what temps are you talking about?
I ride a lot in the fall and winter, and as you mention chemical warmers, you must be dealing with near freezing temps and rain--a particularly yucky combo for comfort, hands or anything, in my experience, and a tough one with long exposure in rain and cold.

I wasnt kidding though about the cost of high end advanced rain and cold gloves, some really are pretty darn expensive.