Yes, you can. I just found the discussion with the details started here: 2.0.6 Chromecast / playTrack
This is awesome!
I put a new GA speaker in the bedroom yesterday and as I opened the door for the dogs this morning I remembered it was about 75% volume yesterday. It probably has a low WAF right now since she is still sleeping. Well what do you know, I can't find the master bedroom speaker on the network now. 
I am now setting up a custom rule to set the volume to a specific level before I play the TTS. I was trying to keep RM simple before so this is pushing me to dig in a little more.
