3rd wan connection correct installation

[SteveLandon]

This may be an odd situation that I have been asked to perform.

1. MX85 in a wire closet 1st floor building, 2 wans in use, primary and secondary. Works well.

2. 2nd floor MS120 -48  connects via fiber cable to MX85, 1st floor.

3. 2nd floor : staff just installed an Starlink business satelitte and Starlink router on 2nd floor near the MS120-48 switch.

4. Need : some method to plug in the Starlink router to the MS120 to get that wan back to where the MX85 and another switch are located on the first floor. Is there any way to configure vlans and port settings to get that Starlink wan back to the MX85 over the switch network?  

[Ryan_Miles]

Is there any more fiber you can use between the MS120 and the MX or a switch near the MX? If not, perhaps something like this which is kind of a hack.

[SteveLandon]

We are keeping WAN1 & WAN2 so this will be a 3rd. No more fiber links available. This 3rd WAN (Starlink) will be tested and evaluated for possible replacement at another of our locations as a backup Internet. I'll have to think on this since the MS120 is hanging off of another switch and that switch is where the fiber is connected. I am worried about the traffic from WAN3 (StarlinK) causing problems on the rest of the network. The only time I can test is very early AM or on the weekend but that's not a problem. 

[Arthamon]

I feel using a VLAN as Ryan recommended would be the best way to go here without running additional cabling.