I’m going to say NO. Since the AVR has no reference to a x.x.1 it has no way of properly rendering any content. Atmos is not simply about birds and planes and rain overhead. The best case, and a looong shot at best would be if they single speaker had dual tweeters and could be wired for stereo. Then you could wire it as top fronts, as in 5.1.2. It would make sound, but it would not be very Atmosy.
I am all to familiar with the “honey Do” list lol, and I’d certainly understand not wanting to go and install new speakers such. However, I am lucky enough to have 7.3.4 in my LR and IMO, any reservations you have with not being worth it will be for nought. Besides, wouldn’t you sleep better knowing your retirement system is all it can be? Lol