SUCCESS!!! Praise Armok, for a breakthrough in dwarven culinary science is upon us!
Okay, while the solution to the sausage dilemma actually turned out to be slightly different than everyone's suggestions (the above reaction actually took a piece of meat and an intestine, and resulted in an identical piece of meat minus the intestine), I have to thank Askot & shadow_slicer for pointing me in the right direction. In the end, I discovered a way to mimic the tanning reaction, and put [MATERIAL_REACTION_PRODUCT:SAUSAGE_MAT:LOCAL_CREATURE_MAT:SAUSAGE] onto the desired meat templates. Then, in b_detail_plan_default, I had to add [ADD_MATERIAL:SAUSAGE:SAUSAGE_TEMPLATE] to the standard and chitin material plans. I did keep [REACTION_CLASS:INTESTINE] on the guts (thanks guys), so my reaction ended up like so:
[REACTION:MAKE_SAUSAGE]
[NAME:make sausage]
[BUILDING:GRINDER:CUSTOM_S]
[REAGENT:A:1:MEAT:NONE:NONE:NONE][HAS_MATERIAL_REACTION_PRODUCT:SAUSAGE_MAT][UNROTTEN]
[REAGENT:B:1:MEAT:NONE:NONE:NONE][REACTION_CLASS:INTESTINE][UNROTTEN]
[USE_MATERIAL_TEMPLATE:SAUSAGE:SAUSAGE_TEMPLATE]
[PRODUCT:100:1:MEAT:SAUSAGE:GET_MATERIAL_FROM_REAGENT:A:SAUSAGE_MAT]
[SKILL:BUTCHER]
[AUTOMATIC]
Now, behold the glory of the sausage!
Before:
After: