I keep a journal, and every time I think of something that makes me say, "Wow, I wish I could say this to T right now..." I write it down. Then, when I finally get to have a session again, I review what I wrote right before and tell my T about the important things I wish I could have told her.
This is a little crazy (but I'm a little crazy, lol), but when I'm alone I will pretend to have a conversation with T. I talk aloud what I would say to her and imagine what she would say to me. It's helpful sometimes when I know exactly how she would respond, but sometimes it's just how I wish she would respond or sometimes I don't even know how she would respond at all, so it ends up making me feel worse. So, that's a hit or miss.