Easy. Make Noguès a little bit more willing to refuse the armistice (he only agreed reluctantly in the armistice because it didn't touch the French fleet or the French Empire) or make the armistice tougher on the French, like for example touching the French Fleet or Hitler give Mussolini something.
You can't have Algérie and Tunisie in different sides. The Résident Général de Tunis (head of the French Administration in Tunisie) and the head of the French administration in Algéria both supported Noguès. You can't have one and not the other, especially given that Noguès was the Military leader of troops in all of North Africa.
The following people supported Noguès :
Georges Le Beau, gouverneur général de l'Algérie
Marcel Peyrouton, résident général en Tunisie
Léon Cayla, gouverneur général de l'AOF
Robert Brunot, haut-commissaire au Cameroun
Noguès was both the leader of the army in North Africa and the Résident Général du Maroc
The following Generals (or admirals) wanted to continue the war (but where either overruled by the public administration or did the same thing than Noguès):
général Legentilhomme de la Côte française des Somalis (Djibouti)
général Mittelhauser, commandant en chef du théâtre d'opération de Méditerranée orientale (French forces in Syria and Lebanon)
général Catroux, Gouverneur Général de l'Indochine Française
amiral Darlan, chef d'état major de la Marine
If Noguès choose to fight, you have all of French North Africa with him, the Levant, the AOF, possibly Djibouti and the Indochine, at least a part of the AEF (Tchad and Cameroon), and with luck, the French Fleet. From there you basically have a scenario similar to FFO, but with a weaker France (less evacuations to North Africa) and with different politics.