I was in a war with my allies against an enemy, and they've won some territories. I'm now suing for peace, and I'd like to demand the provinces they won to be ceded to them. Is that possible?
I don't remember this happening before patch 1.2, but now it's certainly possible. You can demand provinces for your allies, and they pay the diplomacy cost themselves, where appropriate. The warscore cost is the same as usual.
Incidentally, returning cores to allies/vassals now gives a significant relations boost: +40 per core.
You have to transfer the occupation to your ally you want to receive it (assuming that the occupation was granted to you to make that call), and then it'll let you give it to them in the peace deal screen, the flag will show who will get the province, which goes to whoever can core it and has the occupation. This might require art of war though.
it's you click on your flag on the province screen below the diplomacy button and pick transfer occupation. Whoever is considered to hold the territory is who gets it when you say you want them to cede a province in the deal-deal.