How to solve for allocating a percentage of total hours logged to a task or issue to multiple clients - for monthly reporting/billing

If have have 50 hours logged to a Maintenance task or issue in a given month -- I need to be able to apply 70% of those 50 hours to Client A, 20% to Client B and 10% to Client C. Billing is not done by project - but by Requests on a monthly basis- so project level billing records won't work. Need the auto calculated .

I have created a matrix report for request that are direct billed to a specific client - but stuck on the to do the allocation.

Suggestions?