Adding a Follower to a Ticket from a User Lookup Field

Is it possible to have the lookup relationship field add the agent/admin selected as a follower on a ticket? If so, how would one go about doing this? I can't seem to figure this out in the triggers, and the only other closely related setup I saw involved adding a tag to the ticket via macro then using a webhook trigger to remove the tag and add a follower from the organization.

here is our specific use case:

The User Lookup field in on the user profile. An agent, when they are going on vacation or will be out of office for PTO, will use the Out of Office app to flag themselves as OOO. Then, they can choose an Out of Office delegate (custom user Lookup Relationship field). When the agent is flagged as out of office and a ooo delegrate is present, then add that delegate to the ticket followers. 

Please let me know if there are any additional questions.