Populating payslip details

We have a number of hourly workers tracking their time in FreeAgent using timeslips. Each payroll we have to take the hh::mm value from the timeslip and enter this as a decimal value in the payslip in the hours worked field, and then manually calculate their pay by multiplying it by their hourly rate.

I was hoping to create an integration that automatically goes through each timeslip, and automatically populates the hours worked and pay from the timeslip.

It looks to me that there is no way to edit the information that goes into a payslip currently?

Would FreeAgent consider adding to this to the API, or alternatively have the function in the software to populate payslip details from timeslips.

Thanks in advance.