Option [+4]

buy a chastity device if you don't already own one, put it on, lock it, then put the key in the an envelope addressed to your home with the cheapest postage stamp your local post office sells.

(tip, take a picture of the key before you send it so if, in worst case scenario, the key is lost, you can get one replaced.)

you could try doing this without a chastity devise (no masturbation at all) and just send yourself a random letter, but beware if you fail.