I don't know if anything I did was proper, but I did just this sort of thing when I was bush flying in a Cessna 180 on floats in Northern Ontario in the early 1990s, and was forced down by a rough running engine (that had a failing cylinder) on an uninhabited lake, with two customers on board (I was bringing out two lawyers(!), on a fishing trip, from a remote cabin about 5 miles away from my landing spot). In my case it was to relay a message to my base, because although I was 80 miles from civilization, things weren't serious, yet.
It was a nice sunny May morning. It wasn't quite an emergency and my main goal was to contact my base to come pick us up, not trigger a formal official rescue operation. The lake I landed on was part of the same outfitter's camp network, and there was a very convenient dock, from which a trail led to another lake, with a couple of the outfitter's fishing boats ready for use.
So, I sent my passengers (who seemed to be amused by the whole situation) fishing while I tried to raise passing airplanes I could hear in the distance on unicom 122.8 and on 126.7. But no joy. Now what to do... set off the ELT? Then I noticed a contrail overhead and thought "I wonder..." knowing that airlines routinely monitor guard when over sparsely settled areas.
I broadcast a PAN PAN PAN call, with my registration, on guard, 121.5. To my amazement, after a few tries a Canadian Airlines flight, the contrail above me, responded and offered help. I was able to have them contact my base on the unicom frequency and advise my location, that all were well, and that we needed rescue due to mechanical problems, before the Cessna's meagre comm radio transmitter faded out for the airliner. I could listen to the airliner talking to base on 122.8 on the airplane's other comm and knew that help was on the way (the air service manager was suspicious it was some kind of practical joke initially).
My boss showed up with the Beaver about 5 hours later to fly us out, and I went back in the next day to help the air service's mechanic remove the engine and fly it out for overhaul.
I took the pic below while preparing a bipod from pine poles to lift the engine, using a come-along. The mechanic is sitting in a boat we set across the floats so he could work. The Beaver showed up late in the afternoon and we manhandled the O-470 into the Beaver by dragging it up poles into the cabin door using the come-along. We flew the rebuilt engine back in about 2 weeks later and reinstalled it, and I flew it the rest of the season.