Just disolve the 1 gram in alcohol, use some sort of Drinkable alcohol with a very high proof... if you can get a hold of everclear that would be great(190 proof). This way you know that the alcohol is safe to consume. Dont use any of the alcohol bottles that you would get at the pharmacy(rubbing alcohol, isopropyl w/e), as it may not be the right kind of alcohol(2 shots of isopropyl can kill you, a few sips can make you blind), or it will contain traces of other harmful chemicals, like benzene.
Im not sure how much alcohol you will need but just add alcohol slow until the gram is completely disolved. Then split the alcohol finasteride solution up into 1/1000, and you have your 1 mg. For example, if it takes you 1000 ml to dissolve the 1 gram, then 1 ml of that 1000 ml will contain your 1 mg. If you end up with some odd number, like 933.45 ml, just dilute up to an easy number like 1000. Welcome to Chem 101.
Then, let the finasteride dry up and snort it!.... lol... no dont do that, you could... but dont. From here, you can seal(air tight) the finesteride alcohol solution and store it and just drink the amount you need of it daily(everclear is harsh I know).
The shelf life of Finasteride is 2 years. So a three year supply is overkill, so throw it out after 2 years. Also, make sure your finasteride is pharmaceutical grade. It probably is, but you want to make sure for saftey reasons.