I'm fairly sure that the various European powers were keeping an eye on him via warships patrolling the area and paying people on the island itself. If he disappears from view for any length of time that's going to cause people to become concerned, if he disappears whilst a body of high ranking volunteers made up of his allies suddenly turn up helping run things in Greece then people are going to start making connections and asking some forceful questions. As others have said Napoleon was absolutely toxic as far as the rulers of the other European states were concerned, the Greeks would be seriously shooting themselves in the foot in my opinion. I could see the other powers deciding to throw the Greeks under the bus since better the Ottomans control the place than a Napoleon-led state.
Simon,
I would generally agree Simon,that it would have been a course of events as you predict,but let's examine detractors that would influence the predictions:
As I have mentioned in the Colonel's Thread:
1) Napoleon could land in Mani,a long mountain range,practically autonomous and with a long history of risings against the Turks and totally controlled by a certain family who later played a leading role in the Greek revolution of 1821.You could lose an entire army and a mountain of supplies there and none would notice...
2) many Europeans,romantics or adventurers volunteered to fight against the Turks during the revolution;Germans,French,English(among them Cochrane George and Byron...) that formed a corps of Philhellenes under the German general Norman.Some more French would not draw special attention at least in the first years...
3) the revolution would take place normally in 1821 so that it would take advantage of the revolution of Ali Pasha of Epirus that was a major diversion for the Turkish army especially when Hursit Pasha took the bulck of the Turkish army of Peloponnese to fight north in Epirus.
4) When the revolutions starts Napoleon would have free supply sea lines because the Greek revolutionary navy had achieved supremacy over the Turks and later Egyptians,Tunisians and Turks in Eastern Mediterranean.
5) That was in very general lines the situation could be developed,the details I could explain although I have outlined a lot in colonel's Thread apart from the training part.The plot that the Colonel perceived was excellent and after the start which he sets the possibilities are endless...