I think the easiest way to do this, is to create a custom transaction including a variant with the payroll area specified. as there is not really an authorization object where you can restrict access to a certain payroll area. (only the payroll control record object comes to mind, but is useless in your case)
if the restriction on payroll area consists of only one value, the custom transaction is a good idea. because if not, you will have to make a different transaction for every payroll area you want to allow to be executed.
