I'm afraid that's not something that we can support yet, although it remains on our list for future consideration. We have to balance that against other requests that may be more widely desired and have no other way to be accomplished manually, though.
In the meantime it is still possible to split revenue manually as Guru mentioned above, and you can have automatic notifications of sales sent to your partners to give them visibility of what is being sold in addition to using those same records to determine their earnings.