WIP - Tracking timekeeper efficiency on projects where write offs occur

Looking to optimize our prebill review process and would like to know if there is a way to track timekeeper efficiency with fewer workaround than we are currently using:

Example Project: Drafting document that includes text and drawings.  Project budget is $7,500

 - Jr. Associate has a rate of $200 / hr and enters 10 slips at 2 hrs per slip = $4,000

 - Sr. Associate has a rate of $300 / hr and enters 5 slips at 2 hrs per slip = $3,000

 - Partner has a rate of $500 / hr and enters 5 slips at 1 hrs per slip = $2,500

Per the above numbers, the total amount entered is $9,500, which exceeds the budget of $7,500 by $2,000.

Per firm policy, time is written down until the budget amount is met based on seniority.  For example, assuming a 5:3:2 write-down ratio, for every $50 dollars of Jr. Associate time that is written off, $30 of Sr. Associate time is written off and $20 of Partner time is written off until the budget cap is satisfied.

Applying the formula to the above scenario, $1,000 of Jr. Associate time is written off, $600 of Sr. Associate time is written off, and $400 of Partner time is written off to bring the value of the total time entered down to budget amount.

We would like to more easily write off time at different levels for different timekeepers so that the total time value matches the project budget amount. We would like to do so in a way that allows us to track the efficiency of the timekeepers by project. 

What options are available to do this in TS?

Our current process for doing so is too inefficient and inconsistent (manual prebill markups, inconsistent application of write-off rules, manual revision of markups by billing clerk, duplication of records to track written off and billed time, etc.)