for the record, i don't now what the best drug delivory is. I know some of the properties it has, but i don't know what oils have those properites.
i've been telling people to squirt 4 dutasteride pills in a 1 month supply of minoxidil, preferably 1 week at a time. i've also adviced people to add 1-2 mL of borage seed oil to their minoxidil.
since you don't want an alcohol base, emu oil may work too. i don't know which oils would cause acne and which would not, though i read that emu oil does not, and costs much more than corn oil.
4 dutasteride pills in rogaine means that even if 100% of the dutasteride is absorbed, your body would get the same effects as less than 0.1/mg day orallly would give. and if only 2% is absorbed, your scalp would get the same effects that 0.5 mg/day orally would bring.
i don't know how much will be absorbed, and am sure it varies with what oil you use or if you use rogaine. I think you can safely use much more than 4 per month without your body getting a substancial dose. I highly doubt you will get more than 10% absorption, and highly doubt you will absorb less than 1% of the dutasteride in your solution. perhaps 8-12 capsules per month would be a good guess.