I wouldn’t say it’s not hackish, so you might have already found those, but there’s a mpv plugin to play VR videos in 2D: https://github.com/dfaker/VR-reversal
And there’s a wrapper to use mpv with the Handy: https://discuss.eroscripts.com/t/handy-mpv-linux-player/28842
I’ve used both (and they work fine) but never at the same time. I imagine it’s doable but you’d probably have to modify the wrapper to pass the correct info for the plugin to mpv.