Invoice module

We create invoices for two separate services, and need two different sets of Invoice #’s.
For example, Service #1 would use IN-10001 and Service #2 would use IN-20001.

There is only one series of Invoice #’s that can be set in the Company Profile (as best that I can see).

Question: Is there any way to set two separate series that automatically increment? (We would also have to create some type of rule as to which # series to use).

Note: Using the Archived Invoicing is not a solution in this case.