Upload model with multiple poses (FBX not working/possible)

Hello,

I’m trying to import a model done in Stud.io into Sketchfab that is supposed to have multiple poses (or animations that only have a single frame, if you will). While Stud.io can export directly to Sketchfab, it can’t do animations or multiple poses, so I have to save every pose as a separate file. It also can’t export to FBX, the only format it can export to can use is Collada (*.dae).
Apparently the multi-file upload for animations works only with FBX at the moment, if at all.
I tried converting the DAE files to FBX but even then the 3D editor shows no animation. Also the model gets screwed up along the way so FBX is not really useable here anyway (basically the majority of the model gets twisted around and is laying on its back while the rest is flipped 180°).
Is there any other way to do this?