Thank you. Very well, here's my plan. I think we can:
1: Establish the joint research project under K8Ps
2: Argue that participating in it is a wizard's right, maybe even obligation, because advancing the magical theory of all civilization factions better allows everyone, including the Empire, to oppose dark magic and the forces of dark magic, something that is an obligation of magisters according to the Empire and which can be argued to be one of the founding ideals of the Empire (which according to the articles take precendence over everything)
3: Argue that, as such, a joint research center would constitute a permanent alliance against the forces of dark magic and destruction (greenskin, vampires, dhar users, chaos), recognizing, as per the ideals of Sigmar, that war against such is greater than other wars. Such alliance doesn't mean involved countries do not war, just that they informally agree by their mere participation (so that no one has to sign anything) that magical research which benefits everyone (against chaos, dhar magic etc) deserves priority over other wars.
4: As per the terms of the above, every involved country can de facto certify its own magic users to join the joint research program
5: Thus, wizards would have the right to participate and even involve others under the aegis of an research alliance against the forces of dark magic, which takes precedence over everything according to the articles, as long as every magister they cooperate with is lawfully recognised by their country of origin.
It won't necessarilly be an easy sell (especially with our diplo), but I think it does bypass the hard stonewall, letting us only concern ourselves with political will.