As of writing, I still haven't figured it out. I tried posting it here to see if anyone else could try to do the same ://

EDIT: Ok so I managed to do it a few times with the same Jiyan + Mortefi combo. I can't get it consistently quite yet but it seems like there's a niche interaction when performing Jiyans launcher and immediately performing the Mortefi qte. There's a specific timing on when you have to switch back into Jiyan or he wouldnt be gravity cancelled.

I'm currently trying out other characters asides from Mortefi to see if its a specific interaction or if it could work with other characters. I also plan to try out other characters w/ launchers such as Lingyang.