Scripted Action Event Trigger on User Assignment

I have what I would assume to be a fairly common scenario where I am wanting to Assign Administrative access to Dedicated VM's assigned to users. It is an Auto-Scaling pool, so the assignments are done automatically by AVD when the user first logs in. This pool also uses Start on Connect. Because of this, I do not have a proper way to assign admin at the time of first use by a user.

Being able to Run a script (ie. Assign Admin rights) at Time of Assignment, or similiar, which would trigger once - Would be ideal. Currently do not have an idempotent way of assigning the rights.