unable to span or stretch across multiple monitors

[bonds]

This maybe more of a feature request, or an ill conceived hope, but I'm trying to use gamescope to play games stretched across 3 (portrait right oriented) monitors, because it would look awesome. So far I haven't been able to pull it off. I've tried: gamescope -w 6480 -h 3840 -W 6480 -H 3840 -b -- thegame and gamescope -W 6480 -H 3840 -b -- thegame and those just lead to games taking up a 16:9 portion in the middle of my main monitor, leaving black bars of unused space, rather than taking up the whole height of the main monitor (which is what I get if I run the game without gamescope), and rather than spanning all 3 monitors and taking up all of their space, like I really want.

Am I doing it wrong? Or is this not supported? I'm running the latest Manjaro with Gnome.