Back when I used to smoke rollies, I kept an orange or lemon peel in the Drum pack to keep it moist. The added "topping" flavor is a nice little bonus. I've experimented with re-hydrating pipe tobacco the same way (but usually just with a moist paper towel or even a semi-dried teabag) and have had satisfying results.
Place tobacco in a bowl.
Using distilled water, dampen a cloth (tea towel) and cover bowl. Check condition every few hours. Stir tobacco around in the bowl to evenly hydrate. Pinch test to see/measure the moisture. Remove and store in sealer jars when satisfied. Works for me.