I have 5 cornies and also have a floating diptube which I got about 2 years ago and forgot I had it and would need to get a sounding valve to give it a try sometime.Not sure how many corny you have, but you can ferment in a corny too - just did a pressurised lager in there - 2 weeks from brew day to pint - is lovely! Just need a floating dip tube. Very easy to swap out and cheap. Though I'm tempted by a replacement lid with the floating tube built in now.
£12.48 | Corny lid Floating Kit
https://a.aliexpress.com/_uf9LzR
I'll def be using your method for the next non-pressurised beer I do though, great idea!