No concrete idea about "not forming", but history is full of opportunities of the "Confederation" to fall apart.
Basically, I'd say let the key members (actual and potential) of OTL's Confederation enter different alliances with other powers (Bavaria, Bade, Savoy, Milan, Burgundy, ...).
Moreover, to eliminate the "trigger" for the formation of the Confederation, let the Helvetian Habsburg territory be split, either among different family branches or between other dynasties.
And finally, it is very easy to remove the name "Switzerland" for the Confederation from history: "Schwyz/Schweiz" was a derogatory name by the end of the Swabian War 1499.