Can I attach the Collar to the spine?

The short answer is no.

The default attachment point is the neck, your stats and the Pet-Crawl animations require that. Otherwise, if you wear the Collar on the spine straight from inventory, your collar will not appear in the correct position.

The LULU Gravity feature will also not work, as there's no way to know where your head is pointing, so the bell will be pointing the wrong way.