Two MACs and two IPs on one physical interface without 802.1q tags

Did a search, didn't find anything that had an answer that closely matched what I'm trying to do.

We use ISE to profile devices as the come online onto switchports. The switches can pull a trick that lets them assign different MAC addresses on an interface to different VLANs where the frames are not 802.1q tagged as they exit the interface. I'm trying set up one physical interface on a TP-Link TL-WR710N to have two separate MAC addresses, each with a statically-assigned IP address on a separate subnet.

Basically I have a device whose IP cannot be changed that needs to NAT onto the guest VLAN and out to the Internet, but I also need to be able to manage the device doing the NAT. Currently an expensive firewall device is doing this with three physical interfaces. I'd like to swap that firewall for this cheap TP-Link so I can reclaim it for use elsewhere.

This is a diagram of what I'm trying to do:

Does OpenWRT support doing this?

Take a look at macvlan. I'm not an expert, but it allows you to have multiple mac addresses and interfaces in a single physical ethernet port.

Thank you. Looks like I have some reading-up to do.