Meta-ethical systems ususally don't supply their own methdology. Deontologists usually work out rules based on some specific deontological meta-rule or "maxim", such as "follow on that rule one would wish to be universal law". Deontologies may vary according to the selection of maxim.

Ah, thank you. This was the point that I was missing; that the choice of maxim to follow may be via some non-deontological method.

Now it makes sense. Many thanks.