UPDD driver does not currently support the i2c interface.
An open source project called VoodooI2C that brings i2c device support under MacOS is linked here. (The location moves around so if this is broken search for VoodooI2C )
Further development has been undertaken to inject i2c data into UPDD to accomplish full gesture support and is available here.
If you already have UPDD installed and working with a real device then the i2c data can be posted to UPDD.
If your system does not have a conventional touch device normally associated with UPDD then we can supply a UPDD driver that defines a virtual device that can be used for injecting i2c data.
The above solution is only useful for technically competent software developers. We hope to add a generic i2c interface into the driver at some future date.