We likely won't have this feature in the IP Camera plug-in. Currently we're working on supporting Pan/Tilt/Zoom and presets for IP Cameras. Other features like IR ON/OFF, Sound, Relay ON/OFF may be coming as well.
The problem is every camera is different and this kind of feature would be fairly low-level to attempt to support across the board.
Have you considered using the ISY controller? It could do what you want. The ISY-994 PRO model has an optional Network Interface module that enables the ISY to talk to network devices and send them commands either as part of a program (that MobiLinc can run) or through a condition you can set (leaving the house, arriving at home etc). If you are interested in the ISY I'd be happy to talk to you more about it's features and how you might go about setting this up. You'd have to know what the network command/address is to turn motion detection ON/OFF for you camera to insert into the ISY.http://mobilincstore.com/system/isy-994i-plm-combo.html