I've been reading a littl emore and it seems it is possible to ignore the screens edid data. Instead I can use an edid.dat file with the values I want.
I think I have to add hdmi_ignore_edid and hmi_edid_file to config.txt
The only thing I don't know is how to create a an edid.dat file with the correct information.
If someone knows (or even better, give me a better edid file) how to do this I think this problem is solveable.