I think that'd be the way to go.
With a bit of luck there won't be any noticeable volume difference between the two sides and you won't have to do any of the suggested tinkering below...
To account for potential differences/tolerance drift, maybe add a trimmer to whichever dual-gang side is the stronger one to bring it in line with the one that's lower amplitude. Set the unity, then pull the trimmer and measure the resistance, you can then replace the trimmer with a resistor — that way it's one less thing to go wrong and your friend doesn't get to mess with the trimmer's setting "by accident" etc.
