UK Employee Paid in Fees

We are just about to start an employment service for a USA University, involving an employee that will be paid "sporadically" 3 or 4 payments a year for developing and presenting a series of lectures.

We were not sure if the person could be genuinely employed or whether she would have to be treated as a contractor or consultant. It suits the client to have the person definitely as an employee. Our payroll department advised that the person could be an employee: but each month even if there is no payment, we have to file a payroll with the UK tax authorities (HMRC).