I haven’t tried this myself, but I think you can create your own shortcut to your desired tuplet ratios. The command is:
NoteInput.StartTupletRun?Definition=4:3
It’s likely you won’t be able to edit this in the shortcut editor as it can’t deal with every function that takes parameters, but you should be able to edit the keycommands.json file that you’ll find in your AppData / Application Support folder.