Able to have it that you have to go through the 861 before getting to 851?

Optimum online provides the 851 with which they require you to use.
We need the 861 because of MAC security.
Is there a way we can have it:
Modem -> 851 -> 861-> Computer. But noone will be able to disconnect the 861 from the 851 and plug a computer directly into it?
Thanks