I suppose I should have done this to start with . . . I checked Makita's website to see if they had an 800 number for tech questions, and they do. I spoke to a helpful gentleman that confirmed my suspicions: no tools are needed for this backing plate. The thread is counter to the direction of rotation of the machine, so there shouldn't be an issue with it coming loose.
I'm going to go re-examine the instructions (again), but I swear there was a section on attaching the plate using a hex wrench and a locking nut of some sort . . .
Tort