What to do with layer of fat on pork spareribs?
Seems like you get the importance of the fat rendering but still want the spice rub on the meat. I would trim the skin and fat off in one piece, if possible, using a very sharp filet knife. (A small amount of fat left on the meat is okay.)

Then rub your spice mix over all sides of the meat. Place the fat cap back on the meat where you removed it. On the top of the skin/fat season with salt or your spice rub and go to cooking.

The fat will render and you should still end up with well seasoned, moist, tender ribs. Bonus, you should get a well seasoned crispy skin. If the skin doesn't crisp enough with the cooking method, you can remove the fat cap when the ribs are done and place it on a pan under the broiler to finish the crisping.