Well basically instead of doing a simple HTTP GET to /admin?camera=cam1&motion=0
you would have to do HTTP POST to /json
and send this payload:
{"cmd":"camconfig","camera":"cam1","motion":true,"session":"your-session-string"}
This would be easy enough if you can use the linux "curl" program on the Vera. The tricky part is the session string. I'm not sure if you can use this command without providing a session string (allowing Anonymous access, and making the Anonymous account an administrator MAY or MAY NOT be enough).