Call to arms

[Pompan]

I managed to diplomatically get a client state during a war with another nation. My enemy has an enclave that I want, but that I can't reach. This new client state of mine however borders this enclave, so I could give them the land in the peace deals. Or so I though.
I can only give the occupation to a subject if they're participating in the war. My new client state did not join the war when they became the client state. I let a month pass but no change.
Can I call my new subject into the war someway? I can't find anything on it. Or can I pass the territory to them during the war anyways?
Looking for a solution that gets me the enclave in the current war.

Edit: The main focus actually isn't the conquering, but that my enemy looses this land (punic rival mission). But they have nothing to release in this region..

 

[DukeLeto42]

Unfortunately no. Unlike EUIV, subjects are individually called into a war when it's declared, not involved by dint of being your subject (it effectively replaces subjects being in your wars but sitting in their own territory not helping).

 

[Herennius]

IIRC, within the first twelve months after a war has started you can call in someone else; after that the participiants are fixed.