This instantly reminded me of the Junkions from the old 1994 Transformers movie. Specifically, that the Junkions had both their humanoid and their motorcycle forms, and when you knocked one pair down, they switched places. To translate this into what I am seeing here, are werewolves with an ability to shift between an offensive "hybrid" form and a defensive mount-like "worg" form as a swift action. As riders or in their "hyrbid" form they receive increased offense and reduced defenses, while in their "worg" form they have increased defenses and regeneration. They operate as grouped pairs, so make these respective bonuses and the swift changing only effective while they are adjacent or occupying the same square(ie: mounted). So the goal is to, once they are knocked down, to keep them separate and break the pair, ie: a rider w/o a mount or a mount w/o a rider is a significantly easier target.
To make this work though, you need to keep the party moving during the fight. The party should be more interested in reaching their goal than fighting the worgs, I'm not sure what sort of party you've got, but play to their interests. All else fails, they're fighting werewolves, and werewolves come from somewhere, perhaps there is a ritual being performed on the unlucky villagers from a nearby town who are being forcibly transformed into werewolves, and then mind-controlled into fighting the party as these pairs I have mentioned. So fighting the worgs and their riders serves no purpose as their numbers are being replenished faster than they're being killed.(adding a new pair every round sounds dangerous). And the various powers the worgs and their riders get stem from this ritual as well, so the idea is to press the party to stop the ritual, and not stand around and engage the werewolves.
If the party holds their ground, force them to move by say, giving the werewolves a push or knockback on a charge while mounted.
Anyway, I hope that gives you some food for thought.