How to run flatpak app on eGPU?

Is there a simple and elegant non-CLI method to make sure that a certain flatpak app (say, VLC) always runs on a certain GPU/eGPU? I looked into modifying the corresponding .desktop files by adding the DRI_PRIME= prefix, though I am having a hard time telling which is the .desktop file to modify thanks to the presence of multiple .desktop files in multiple folders for the same flatpak app. Note that this method should ideally be resistant to app updates–i.e. produce results that persist through app updates.

Anyone?

Answer: Using Flatseal, set DRI_PRIME=1 in the “Environment“ section of the application (VLC in this case) by clicking “+“ in the “Variables“ tab. (Note that this assumes that the eGPU has index 1.)