I have thought of a few methods they might accomplish this. The easiest, mechanically, is to give him spells to accomplish this.
Some details about the campaign/fight (major spoilers for Paizo’s Ruins of Azlant AP)
What are the best 5 arcane spells for area denial? The area to be protected is a control panel that can be reached from two adjacent squares; there is also a hallway leading into the room that they will need to travel through that is 10×10 and 40ft long.
Some members of the party have inanely high Saves, especially against spells, so spells that do not require Saves or still have some effect with a Save should be considered stronger than similar spells that do. The party, as most high level organizations do, have easy access to Freedom of Movement.
Directly related to my question about doing it with narrative.