Hi @malcolmlewis and @SJLPHI !
Yes, I found that instructions (I think the opensuse official help pages are even better: SDB:NVIDIA_the_hard_way:Installing_NVIDIA_with_Secure_Boot), however it seems to apply just for the nvidia driver “installator” itself, and not for the cuda “installator” (that installs the driver by default): I don’t find a way to pass such instructions in the last one.
It is not “bad”, but it is most definitely “ugly”.
So many details that make worder and hope you are right and that:
really happens in some way that we can keep the discrete cards. 
Also, as I mentioned I tried too hard to install it from the repos on 15.5, so I gave up for the hard way (that worked in the first attempt provided that I disabled the mok, which is an ugly solution).
So no ideas on how to get rid of the “unsecure” messages on boot? At least not having to deal with two different “installators”, cuda and driver?