I'm an idiot...
I wasted a bunch of time trying to come up with a way to hack into a terminal on the surface so I can flash a message to the colonist wandering around our ring, and then it hit me-they had on an exosuit, which means a visor with heads-up displays.
I realized I can broadcast directly into that helmet, and put information right in front of the colonist's face!
I decided to try beaming a line-of-sight message at them by hacking a nearby infrared laser cluster..
I'm no communications expert, but the risk of a free space optical signal being intercepted seemed minimal and I figured it'd be hard to jam at short range.
What if doing this gives away my location, though? It occurs to me that our invader might be using this colonist as bait...