Controlling X10 via analog input is possible using the on-board rules. This would work whether the module was online or offline.
To get started: Click Modules tab, and select the Module that has the X10 smart board attached. Click "Onboard Rules" tab.
One of the Actions for a standard rule is control X10. You can also add a condition based on the analog input value. I would also add a condition testing a Variable Value, so that that the IO-204 does not continually send the X10 commands.
This project would be like the Servo project on the wiki:
http://www.iobridge.net/wiki/onboard-actions