A stronger ducal caste might help along the way ... If i recall my history correctly (which admittedly i very well might not, as its not in the period that calls my interest), the primary difference between France and Germany before Germany degenerated into the emperor 'merely' being first among equals by the time Salian came around, was the regency of Otto II under a unpopular Queen Dowager, which led to the nobility gaining a lot more independent power ... paired with unstable border provinces, specially to the north and east.
If France could get something similar with a long regency, while having a more unstable border into Iberia (France having a stronger, earlier control of Barcelona and Navarra might do this). But it would have to be early enough that France as an independent nation, haven't solidified just yet so, so by the time 900 comes around I'm relatively certain it's to late, as the lines are to distant unless someone decides to marry the lines together and accidents happen to make it one of a scant few acceptable choices for succession