Two parts to the question: the legal and the behavioral.
Sorry, I couldn't resist.
The legal question is whether or not you need to pay for an additional provider. That is between you and AC, but I certainly think that you can make the case that this is a part-time provider with a limited schedule, who presumably won't even be generating notes (i.e., essentially just using the scheduler), so you shouldn't have to pay for a license and support for them.
The second issue is how to set it up. AC will let you set up as many users as you like, even if they are not true providers. So you can create a user called "Neuropsych Test" and use it to schedule patients. The user must be at a provider level to have a schedule.
