https://developer.valvesoftware.com/wiki/$poseparameter
Pose parameters would be a very nice and extremely handy feature. I've worked with them in the past and handling it natively within 3DS Max and Worm Wall would be absolutely amazing!
Pose parameters are depreciated and handled through the '$sequence blendlayer'
https://developer.valvesoftware.com/wiki/$sequence
This adds the ability to control the armature on a turret model for example..
http://gamebanana.com/tuts/11915
I'll look into adding the param.