Use a non player character as the character to spawn and spawn type as matrix and actor type player. Also detain the main character so there is no interaction with him.

Thank you, that worked great!

For anybody else interested in this the exact steps I did were:

1. Create a camera region around matrix part of map (as usual)

2. Add an actor spawner to the matrix part of my map, overriding values as follows:
- prop name: actorPlayerMatrixPersona
- spawn at map start: False
- spawn type: Matrix
- scene dimension: Matrix
- actor type: Player
- actor name: Persona (but I set this dynamically later, so not necessary)
(Didn't even mess with character editor)

3. Create a trigger fired when I interact with workstation with these Actions:
- Detain (Single Actor: Player Character 0) into Manual Detainment
- Activate Persona: actorPlayerMatrixPersona spawner
- Set (Single Actor: Persona: actorPlayerMatrixPersona to be Player controlled
- Teleport the camera to Persona: actorPlayerMatrixPersona
- Set (Single Actor: Persona: actorPlayerMatrixPersona)'s display name to ((Player Character 0's display name) + ('s Persona))

Notes: This allowed me to use a non-decker character in the matrix, and simulate the matrix avatar, but I didn't do any matrix combat with ICs/ESPs/etc (however normal triggers and interactions worked fine). This was a single-player scenario (no henchmen). I probably could have used Triggering Actor instead of Player 0, but I didn't. I didn't test exiting the matrix since in my case the next scene progresses from here, but theoretically would be sorta of the opposite: disable/destroy the matrix persona and shift camera back to player character, and un-detain the player character by using "detain player 0 with freedom".