Add only Selected VDOM in Fortigate to FMG

Hi, Just want to ask, I have 60 Fortiwifi and FMG with 100 managed device license enabled. And due to configuration issue, I want to enable 2 VDOM in each fortiwifi. But this second VDOM didnt need to be managed centrally. It is used only as hardware switch type between 2 interface. Can we add only root VDOM to FMG to avoid licensing issue? Thanks Andryan VT