Run GTAV and Livesplit at the same time

Ok, I want to use the "Run EXE in prefix" functions, however Heroic runs wineboot -i before running the exe, which makes it wait until the game is closed, I want to have both the game and the exe running at the same time. How can I run Proton manually in the same prefix heroic uses? I already found the command in the Heroic logs, however I couldn't manage to get it working, if I replaced the legendary launch command it tried to run the exe without proton for some reason.
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Run GTAV and Livesplit at the same time - Heroic Games Launcher