Nokia 7210 SAS-K5 Question

My ISP (Cox Business) installed a Nokia 7210 SAS-K5 at my facility, and they assigned Port 5 as the copper hand off. I am currently using a single router (multiple static IPs), but have been looking to set up a secondary/backup router in case the primary fails or for when I need to do periodic maintenance. I could insert a switch between, but that seems to just be adding another possible failure mode, which I'd like to avoid.

Can the SAS be configured to also allow Port 4 in a switched configuration so that I can have two routers attached? I know it'll ultimately be a question for the ISP, but for now I'm curious if it's even technically possible given the hardware present.