You could always add a cereal filler to reduce the amount of fat used, i.e., finely ground oatmeal or rice - not flour. You would also need to add ice into your mix as you grind to keep the meat cooler and the grain moist. This would keep your sausage together and keep the fat content very low. Commercial grinders often do this to reduce cost, and, most lowfat sausages use some type of cereal grain.
Good luck,
DD