State Tax Allocation for Hourly Employees

We have a couple of hourly employees who work in more than one state and we need to allocate their wages to each state for tax purposes at a fixed percentage (for example, 80% in DE and 20% in PA). For salaried employees we can use the Tax Distribution screen to split their wages out on a percentage basis to each state.

However, when we try to use this screen for an hourly employee, we get an error message that says they can only have one distribution at 100%. Peoplebook says the tax distribution can only be used for salaried and exempt hourly employees.