I work for Vokera, we wouldn't support another brand OT control on the boiler officially but I'll help and be interested in how you get on.
Two things first on any OT control on the Linea One, open the boiler control box cover to see whether there's an unconnected ribbon cable, about 1/2" wide, this will be needed for OT, sometimes it's not included with the boiler. You'll also need a small interface board to control it OT. I can get you the part numbers Monday.
OT wires and the ribbon cable go into the interface board. cables included in the box in which the board comes should be discarded.
If you have facebook look for the Vokera BeSMART group, there's an instruction sheet I wrote for the Linea One.