"No precedent"? Right of conquest is a well established precedent. In any case heres a few ideas.
Pick the title for your noble to be and pay some people in the area to start calling her that, hopefully it'll catch on (tell a lie loud enough and long enough and people start to believe)
Whatever noble council that determines eligibility will probably breakdown as 30% for 30% against and 40% pragmatic. Find out what would sway the pragmatists be it bribery, blackmail, or whatever.
Does the parent nation have a king who makes those decisions? Get them on your side, new royal taxes should be welcome.
Explain to your alleged hard nose DM that this is what the group wants.