Dear John,
In the installation manual of the Modbus interface at page 10 are the registers you require. Manual here.
I just hang up with a Daikin Technician (service guy from Daikin directly, not dealer), he said it should work and promised he will further investigate at Daikin’s HQ. I’ll keep you updated.
It’s definitely easier to have rs485 installed! Forget about KNX just for one interface (been there done that! 
)
LATER EDIT: the guy called me back. The answer is that for older CA models the modbus interface works. For the one that you have EHVH11S26CB9W it does not. The only option they support is KNX. But in 2017 they plan to issue a LAN adapter for your model. Sorry for the bad news!
BR,
George