Assigning of multiple cost plan type in Billing Extension

How to assign multiple cost plan type in percent spent revenue method in Billing extension to generate revenue using two different Financial Plan type.

Requirement: Client having two different project classifications and each having different financial plan type. They are generating revenue based on Percent Spent Revenue method.

In the below screen, I have option to assign only one cost plan type.

How to assign both the financial plan type (cost plan type) in Percent spent revenue in "Manage Billing Extensions"?