Can you add interfaces from a FortiSwitch to a software switch on a FortiGate?

Hey everybody,

Is it possible to add the interfaces from a FortiSwitch FS-108D-POE (3.6.2) to a software switch on a FortiGate-60E (5.6.2)?

I'm assuming no, as I've doing some pretty extensive Googling and came up empty.

Or, does the 60E just not support it?

Thanks in advance for the help!