I'd say a worse French performance in late 1805 (especially in Auterlitz) would be a useful POD for that. If austria is a tougher nut to crack, but Napoleon manages to get the upper hand on the field without taking Vienna and have the treaty of Presburg, he would probably offer a lenient peace to Austria and maybe wreck the Third Coalition in the process. You could have some bargaining between France, Russia and Austria on those terms :
- France comes back to the borders defined at Lunéville, keeps indirect control on the Netherlands and Northwestern Italy ;
- The HRE would likely be disbanded in its old form, but Austria would be awarded proeminence in Germany, probably in a tight alliance with Bavaria ans Saxony, Baden and small german states in Northern Germany being more of a French-Austrian condominium. Austria keeps its Italian gains
-Russia would have some compensations, probably at the expense of the Ottoman Empire (Napoleon would look elsewhere).
France and Austria make an uneasy, but workable alliance, each partner having one or two threats on his back (Britain for France, Russia and Prussia for Austria).
Two losers ; The UK and Prussia. Those two are likely to make a counter-alliance, probably with Russian benevolent neutrality.