I don't think so. When a game is fullscreened, it basically tells the os that it wants full control over displayed elements. It would require a very elaborate hack to put something between the game and the display. A hack that would most likely crash the game or be detected as a cheat.
Like I said, you may be better off buying a front panel display.
But you are probably the only user who has ever come up with this idea and as there has (probably) never been a need in the past nobody has bothered to waste time trying to write suitable software that only one person is likely to use. Just my very random thoughts of course. My advice is forget it and get a pair of decent headphones!
In this article it looks like 3RVX should be able to do what you want.
Source: 3 Volume Control Tools With Pretty On-Screen Displays - Instant FundasIf you intend to use it when watching movies or playing games full screen, make sure you disable the setting ‘Hide when other programs are fullscreen’ under the Display tab of the program’s settings.
I don't know anything about this program, but you can check it out.
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