Adding zero effort features to Releases > Roadmap (Gantt Chart)

I would like to add a zero effort feature onto a Gantt chart view, and give this feature a duration over which it will be completed.

Currently when you add a zero effort feature and then give it a duration, the effort estimate automatically increases to reflect the duration you will complete task over, say 3d. There is a work around to set the effort estimate to minimum increment, 1min, and then add to the Gantt chart, but I would like it more clean than that.

Reason for this is that sometimes I wish to add features and assign to resources who are not part of my overall capacity and budget (eg non billable sales resource or a customer resource), so I do not need to track their effort, but want to track progress against their features which mine are dependent on.