Using Multiple Rate Types

I am preparing Bid Plans for a client who has a large number of customers to who they provide staff resources at a range of different rates. E.g a named planning engineer may be cost by an hourly rate to various customers as follows:
e.g
Rate 1 – Internal cost =£35 / hr
Rate 2 – In-house company = £38 / hr
Rate 3 – Government Client = £40 / hr
Rate 4 – Rail Engineering Client = £45 / hr
Rate 5 – Competitor as Sub-Con = £42 / hr
Rate n – Pharmaceutical Client = £?

Since P3e only allows 5 rate types, I am restricted applying rates for a 6th or nth client. I cannot change a rate type since they are being used in live projects and this will make a mess of the cost reporting for these schemes.

I want to have more rate types available for the same resource, how can I do this without creating a new resource library for each project? Any good advice on a practical and workable solution would be welcomed.

Paul