I mean this in the nicest way. I am having trouble understanding questions about "what to do with" St. Louis trimmings. By that I mean the questions seem to imply that one needs to do something separate with the trimmings.
I don't really need to do anything different with them. I've done St. Louis cut now for about 6 or 8 rib cooks. One just last Friday. I did 3 racks of "Chinatown ribs".
When I St. Louis cut my spares I am just breaking down the full spare into it's component parts.
This doesn't mean that one needs to do anything different with them. The "rib" part that's left presents almost like baby backs but with more meat and flavor than BB in my view - just like spare ribs in general. In a sense St. Louis cut spares are just bigger, meatier baby backs.
So I am actually doing St. Louis cut for faster cook time at a given temp as well as going for the (to me) better presentation than a whole, untrimmed spare rib rack.
Other than the St. Louis ribs you have tips, skirt and the point. If you leave the point on it's St. Louis, if you trim it off I believe it's Kansas City style (which I do).
Cook all the meat at the same time, just as you would if you left the spares whole. I place the ribs on the top rack and all of the cuttings on the lower rack. I marinate or rub all together. I don't separate out the other cuttings for use later at all. No need to (unless you specifically want to).
So - rib cuts on top all other meat below. But - mix them up how you want, really doesn't make any difference.
I will take the skirt and points and cook them in foil to help keep them from over cooking, but other than that the tips and breast bone go right on the rack. All gets foiled at the same time and unfoiled at the same time. The skirt and points are "tasters" during the cook or right after pulling.
The rib tips and breast bone cuts get chopped in 4" inch or so sections and get served right along with the "ribs" for those who don't mind a little picking. They are really flavorful since they have more fat. The meat pulls easily from the fat, making them easy to eat.
That said people will tend towards the ribs. The tips and breastbone that's left get eaten with the leftovers. I just finished a plate full of rip tips about 30 minutes ago. There's none left now
Otherwise I'll pull the meat and save for sandwiches or mixing with pulled pork.
So I don't save the "other" pieces for cooking later ever. I always cook everything just like I would by cooking the whole spare rib plate.
Most times there's no left overs. Only when I cook way more than I need will I end up pulling and zip locking.
I'd much rather cook everything at once than saving/freezing the other pieces for cooking later.
What I may try next time is cooking the ribs sections with the primary recipe I'm playing with and cooking the "cuttings" with my standard rub, etc to split things up for later.
So not trying to offend, but there really shouldn't be any question with what to do. The cuttings don't suddenly become anything different or somehow a problem just because they are now separated from the ribs themselves? It's what is typically cooked with the spare rib plate when cooking whole.
Treat, cook, serve them the same and cook them at the same time as the ribs.