I've been to the dealer and he told me that as I've got Stage 1 it's not possible to install it : I have to choose between EITMS or stage 1. Is that true or is it just he doesn't to do it because it won't bring him money. 
Other thing, is it really useful to have it cause I mainly drive in the city pretty hot and with a lot of traffic ?
John, the CVO bikes automatically came from the factory with the Stage I calibration, so I'm not understanding what this guy is trying to tell you. There should be two calibrations, both considered Stage I for the stock CVO 110 engine, one to turn the EITMS on and the other to leave it turned off (stock). If they connect your bike to the Digital Technician computer system they can get a list of all the available calibrations that are approved for your bike. As best I can tell, there should be at least two choices, the stock calibration and the new one with the EITMS enabled. Harley paid to have this new calibration downloaded to the bikes during the warranty period, once the bike is out of warranty I assume the dealer could charge you his going rate for downloads. Here in the US the usual price was $149.
Do you have a phone number or address for the Harley representative in your country? You may have to talk to someone there to get a good answer, if your dealer can't help.
Jerry