On the Vezelay route, there is a (probably unmarked but recommended) route to Irun and the Norte From St-Palais via:
Armendarits, Ospitalia, Itxassou, Espelette, Pont d'Amotz, Sare, Ascain, St-Jean-de-Luz and Hendaye. You will need good 1:25000 IGN maps. The route is reckoned to take 3-4 days.