Allow certain users to delegate workflow?

Summary:

Is there a way to allow certain users to delegate their workflow? We'd like HR assignees to have access to Delegate workflows to other users but not allow managers access. When we use the Delegate action in BPM workflow, it's turned on for all assignees. Alternatively, we've tried disabling delegate at the BPM task level, and enabled a vacation period, however that causes the workflow to error with user doesn't have rights.