You didn't say what bike you have, but I'm assuming you have a Heritage Classic. If so, yes there is something you can do. go to www.gotsaggybags.com and you can order an insert kit for around $125. There is also another company you can send your bags to and they will do this for you. (I can't remember what their name is tho).
Just had a look at that site what a fantastic result .The bags look better than new ,I have Armorall and a few other good quality leather conditioners but they dont have an agent here in Auz for the sagging bags. I have just emailed them to see what they can do and help me out. Can anyone give any suggestions about keeping the rain out of the bags ? Cheers Dazza