Feature Request: Pass the output of an external command to an internal one

While in Broot, I want to use Fzf to manage some bookmarks. It'll be nice if I can run Fzf and pass the output to :focus. I can't find any workaround for this.

Perhaps something like this could be implemented?

{
    invocation: bookmarks
    key: "'"
    commands: [{
        execution: ['sh', '-c', 'broot $(cat ~/.config/broot/bookmarks.txt | fzf']
    }, {
        internal: ':focus {stdout}'
    }]
}