Why not create one list for the leads to go to for this launch to promote to and continue your JV agreement (50/50) in regards to that list. This way the lead only receives response from their actual opt-in and both of you effectively keep 100% of the leads.
In other words, the two of you would make an agreement on the creation and management of the particular list as well as for promoting to that list and share the proceeds generated from the list.