Calculate Activity Price with Qty(volume) Activity fixed

Dear experts:

Scenario: I have a fixed capacity of 100 hours in PP

I have a customer that desire calculate the actual price of activity with Actual Cost / fixed volume activity. Currently I know that  KSII(actual price determination) takes the actual volume confirmed by production. Price = Actual Cost / actual volume.

Thus independently of quantity activity confirmed by PP the customer desire that 100 hours to calculate the actual price.

Anyone know how do I do it?

Thanks.