I would just like to point out to everyone that the only ones who really wanted a Palestinian state were the Palestinians. King Farouk of Egypt wanted to annex the Negev region while Transjordan wanted a port on the Mediterranean Sea. Syria and Lebanon both wanted pieces of Northern Palestine. Iraq even wanted Palestine to be part of a fertile crescent under Iraqi dominance.
To put it quite bluntly, no one gave a damn about the Palestinians. The Arab world only started supporting the idea of a Palestinian state in the 1960s with the formation of the Palestinian Liberation Organization.
Shoot the Mufti, allow unrestricted Jewish Immigration don't arm the arab states. 2 out of 3 probably work.
Or better yet. Don't make Amin al-Husseinei the Grand Mufti in the first place. There was a four-way election between Al-Husseinei and three members of the Nashashibi clan. Al-Husseini won the fewest votes, but the British Commissioner to Palestine, Herbert Samuel, was desperate to keep a balance between al-Husseinei and the Nashashibi clan, a member of whom had become Mayor of Jerusalem. Eventually, Nashashibi front runner Hussam ad-Din Jarallah withdrew from the race, moving Al-Husseinei into third place and under Ottoman law, he won the position of Mufti, though he demanded this be changed to Grand Mufti. He would become leader of the Supreme Muslim Council the next year, becoming the political leader of Palestinian Arabs as well.
The Nashashibi clan, unlike many of their contemporaries including Amin Al-Husseinei, was one of the more moderate factions in the dispute between Palestinians and Jews after World War II. They supported British proposals, such as the partition plan of the Peel Commission in 1937 and the 1939 White Paper. They felt that the Arabs would be more likely to achieve their goals by working within the Mandate system.
Maybe have Abdullah of Jordan sign a non agression pact with the Zionists
According to The War for Palestine: Rewriting the History of 1948, the Jewish Agency tried to negotiate a deal with him in which he would annex all of the Arab areas of Palestine (equivalent to about 39% of the region, I believe) in return for Jordan not invading Israel, but Abdullah refused to commit 100% to the deal and he was eventually cowed into joining with the other Arab states with the invasion.