Distribute hours

Alright, I have a tough one here. What I am mainly looking for is a way to automatically distribute hours based on a maximum number of hours per month and per year.

Base assumptions: 2000 hours (includes holidays) in a work year. 4 of the customers pay 33% and two pay 18% (roughly).  The total number of hours can exceed the normal work year as long as it doesn't exceed 36 hours so 2036 is the MAX. I would like to keep it as close to 2000 as possible (but the way the math works I know it's not always possible). So that's what's shown in the first table.

In the second table, I've added in some travel hours that come from another source. So if someone was travelling for Customer1 they would only charge their time to that Customer and then the remaining hours would get distributed across and down.  

I was wondering if there was any way to automate the distribution of hours.  I put in a table for the total number of hours per month if that helps with the formula. Thank you.