Boss made a PD-1 distortion pedal that does that. Interesting, but I don't care for the sound of the distortion.
If I were going to go about this, I'd probably take a wah or volume pedal and rewire it myself to sweep between two different loops. I'd probably try a dual ganged pot so I'd be seeping both the input and output of each line (clean/distortion). Hard to say what would be the best way to go about this without trying a couple of different ways though. I'm not an electrical engineer.
Also, I always hate how so many people always say "use the volume knob on your guitar" like that's the only right way to control overdrive. There are so many ways to go about this, and none of them are wrong. It's as valid as any other for sure, but by no means the best. It's also not the "purist" way to control OD for all you elitists out there. That would be controlling dynamics with your hands by picking and fretting with sensitivity, just like people have been doing for hundreds of years on acoustics.
... Sorry. Narrow mindedness, especially from the old guard, is a hot button of mine. And my rant wasn't directed at anyone here specifically. It's just a common theme among questions like this on the internet.