We used to add small amounts of breadcrumbs (unseasoned) or instant potato flakes to our sausage mixes before stuffing into casings- it helps retard water loss. But as someone above pointed out, the secret to juicy sausage is to go heavy on the pork fat.
You are right. Fat makes the sausage.........there can be no substitute. I toyed with fat-free brown gravy for years, to the extent my dogs won't even eat their Kibbles doused with it. Fat is just as integral part of the gravy as the smashed potatos sitting under it. I guess some things are worth dying for.
Ya'll smoke your sausage? I've Aggie-engineered a great backyard smoke house.......portable, and easily disassembled if ya can't spare the room after the sausage making routine. Un-smoked sausage is sorta like an un-lit cigarette, why bother.
Stews, soups, chili, pots of beans. Great places to slice up those sausages into chunks and really enjoy them. Send some my way. Seriously, this is why so many hunters add pork fat to their ground venison (be it sausage or just ground meat). Don't give 'em up, just put them in a dish that has more liquid.