(1) What is the point? Does anything block when you start a "foreground" command from a shortcut? What aspect of "foreground vs background" are you after? (2) In a shell
& is interpreted by the shell. Maybe the functionality of custom shortcut does not use a shell to run commands. There is probably a way to run a shell (that will run the desired command), but please respond to the first part of this comment before we create a possibly unnecessarily convoluted solution just because.