NOTE: As of 8/3/17: There is a known bug that the vendor is addressing so you cannot currently do it.
FOR NOW: Correspond by email or phone as you've done in the past. Alternatively, contact SPO who can give the person access to the record so they can at least log in and view the entire proposal in Kuali. This doesn't add the person to routing, it only gives them view-access to the record.
SCENARIO: Chip Lenno is added as an Ad Hoc Recipient - APPROVER because the proposal involves a new server. Chip delegates server analysis to Steve Mann. Therefore Chip wants to add Steve to the proposal as an Ad Hoc Recipient so Steve can view the proposal in Kuali and analyze support ramifications before Chip approves the proposal.