Fortiextender in SDWAN

I was wondering if anyone had used a fortiextender in a SDWAN configuration. At the moment my 40D is plugged in to a 61E at a remote site. I was hoping to set a second 40D with another carrier and then put them in a SDWAN. The current 40d is plugged in to port 1 of the 61E which is still part of the basic 7 port LAN switch. This means that the port cannot be added to the SDWAN at this point. I'm guessing I need to set the two 40D to WAN1 and WAN2 (information on how would be good) or maybe isolate port 1 and 2 away from the LAN switch but unsure what to set them as. Any help or info would be appreciated. 

thanks