You'll probably just have to hunt around the for activity that starts power save mode and set it to activate whenever criteria are met.
I use Tasker for wireless charging. I have one set up in my car and nightstand, so when it gets set on them, the screen timeout is set to 7 seconds and then it starts to Daydream.
I'd love one for turning on FoxFi when it realizes it's connected to a computer... But it's impossible to contact the devs. I wish they'd make it so we could launch each activity ourselves. Or at least make a plugin for it.
Sprint Galaxy S5 SM-G900P
Samsung Galaxy Note 10.1