Splitting the Cost of a project task between 2 contracts

Summary

Is there a way to split the costs pooled against a specific project task to get billed in 2 different contracts

Content

We have a scenario where the costs gets booked into various task in one specific project.  Some of the tasks in that project gets associated with a contract and some tasks gets associated with a different contract.  This is possible since the specific tasks in the projects exclusively for a specific contract.  But there are also a few tasks, the costs against which needs to be split between 2 contracts.  The key here is that they need only one invoice to be generated for the contract.