Hopefully, your vendor will adopt MFA and a zero trust model; but in the interim you are going to have to do it the tough way.
You need to put something in front of the VMX to perform NAT. I typically use an Ubuntu box. Behind this, you put the VMX. All traffic has to go through the Ubuntu box to get to the VMX (so the Ubuntu box will need a port forward to the VMX). Any traffic leaving the VMX will be NATed to the IP address of the Ubuntu box, so from Amazon AWS perspective, all traffic is coming from the Ubuntu box.