the only way really possible is to keep the Jews from ever losing their ancient homeland
Riiiiiiiiight. Because every people in history that ever lost control of its "ancient homeland" and didn't get a new homeland somewhere else invariably returned there, never ever assimilating into other populations or settling down later on and establishing a homeland somewhere else...
Oh. Wait.
But to actually answer the OP: zionism can very conceivably be changed into something very much like you suggest. Any POD that makes Europe less antisemetic in the 19th century would do wonders. Napoleonic victory, for instance, would get you that result (Nappy was big on religious and ethic tolerance, opening up the ghettos wherever he went).
Succesful 1848 revolutions in Germany and several other states would also work (again, the liberals at that time were all for tolerance).
In such a less oppressive Europe, Jews would be less inclined to leave. A certain 'awakening' of the Jewish identity is still likely, because that sense of ethnic unity was actually
inspired by the French Revolution and the patriotic revolutions of '48. But with Jews generally enjoying comfortable, succesful lives in Europe... well, they wouldn't be mightily inclined to go settle the dry, underdeveloped land of Palestine, now would they? A ceremonial once-in-a-lifetime journey to Jerusalem would suffice, and 'zionism' would indeed be more of a cultural-spiritual affair.