About the issue in question.
If it were up to me I'd institute wide-spread structural changes throughout Pakistan starting from:
(i) enormous autonomy to each & every single Province or Federating Unit of Pakistan because of which they're practically Independent Countries with only Foreign Policy, the Armed Forces & 1-2 other Portfolios being controlled by the Federal Government !
(ii) abolish the National Assembly of Pakistan & replace it with the Senate as an elected body of the Federating Units/Provinces of Pakistan on an equal basis for all Provinces & Federating Units with 1/4th of the seats being for men, 1/4th the seats for women, 1/4th for the religious minorities & 1/4th purely on merit !
(iii) that the Federal Government is weak but the Provinces/Federating Units are Strong - a little like Switzerland !
(iv) abolish the AJK President & PM's post !
(v) hold a plebiscite in both AJK & GB on whether they wish to stay with Pakistan or whether they wish to join India (under the auspices of the UN) - Something that India will most certainly oppose & it won't go through but we'd place our desire to end this issue once & for all on record nonetheless !
So follow that up by making both AJK & GB as de-facto Provinces of Pakistan while including a clause in their respective constitutions (I want each Province to have a sub-national constitution) that their final fate be linked with a plebiscite to be held in Princely State of Jammu & Kashmir !
Have the above vetted by people from the UN & incorporate any changes that they propose so as that isn't prejudicial to the Kashmir Issue !
If the Sino-Pak Border Agreement isn't prejudicial to the Kashmir Issue because it includes a clause that border will be revisited once the final solution to the Kashmir Issue is arrived at, I don't see why the UN would find this prejudicial especially if GB is already a de-facto Province !
(vi) follow that up with massive development in GB to truly make it the Switzerland of the East that it is !