Nice idea!
The way you set things up will only execute the scan() routine once (when you press the FB 4 times).
You need to call the scan() routine from the loop() routine so that it is executed repeatedly. You could create an additional mode (for example MODE_SCAN) for this so that the standard doTuning() is not executed while you are in scan mode.
If many users think this is a useful feature we could perhaps include it in the next version. Any votes?
If you are on Github, please create a fork so that I can merge your code once you got it running.
73 Allard PE1NWL