You could have two instances of Steam installed; one logged into User A and the other logged into User B. As far as I know, you can't have a singular copy of Steam have two instances running on the same [computer] account, BUT two different computer accounts can use the same installed copy of Steam (basically run the Steam installer twice installing to different places).
All you have to do now is not use the
steam://run/appid/xxxxx shortcuts, but instead use each specific instance's
"[Path to Steam with User A logged in]/steam.exe" --applaunch 730 and
"[Path to Steam with User B logged in]/steam.exe" --applaunch 578080.