I've got to try menthol crystals. How much would you use? Peppermint oil or peppermint extract is probably safer though than pure menthol.
For sublingual dosing of anything, I don't like alcohol. It burns a lot. I think DMSO is better, and it's solvency tends to be higher than alcohol for a lot of compounds. There are many alkaloids that are more soluble in DMSO than alcohol. Plus it tastes better than alcohol.
Salvinorin A absorbs much better sublingually with DMSO than with alcohol. It even works better in acetone than with alcohol. Alcohol works better for some other alkaloids though. It all depends on the solubility of the alkaloid.
If you want to open up the blood vessels, try adding some calcium hydroxide! It burns just like alcohol and opens up the blood vessels much better than alcohol does. Plus it doesn’t taste bad. That’s why it’s used for betel nut chew, coca leaf quids, and other similar sublingual drugs. If alcohol worked as well, they would use alcohol, but they don’t, they use a tiny bit of calcium hydroxide (always wrapped in leaves to prevent direct contact with the mouth to avoid ulcerations).