The one thing that I absolutely do not recommend is to simply store the excess food in your tent. For one thing, if the NPS rangers catch you doing that, they may ticket you. The bears just love it when you store food in your tent, because they take great joy in ripping a tent to find out what smells so good inside.
I've done trips where I got most of my food inside the canister, and then the excess was loose in my pack. But then I ate the excess on the first day and evening, so by nightfall everything fit into the canister.
If you absolutely must get a second canister, then consider one of the small ones, like the Bear Boxer, a.k.a. Bear Box Contender. It holds only a few days of food, but it will fit into a smaller pack.