Do I have to configure anything special to use shellPrompt with extra args?
For example "xterm -e emacs -nw" won't start anything and I believe it's
because shellPrompt wants just a path or name of something in $PATH.
I'm not exactly sure what you're asking, but shellPrompt uses "spawn" so should not have issues with extra arguments. I do see an issue where completion would break if an executable has a space in its name, but that shouldn't affect running it if you have your quoting correct.