Create your own route

I don't understand what you mean by "official". The only official recognition I am aware of is the Compostela offered to all who walk the final 100km into Santiago. I believe that you can also ask for a certificate which states the distance you have walked. I walked from my home in the UK to St Jean Pied de Port by a route I worked out for myself. I also chose to walk from Canterbury to Besancon by a personal route before joining the main Via Francigena to Rome. In both cases I found stamps occasionally in hostels and tourist offices. I did not worry too much about gathering proof - I walk for the experience.

You may find this site useful www.ffrandonnee.fr. for routes, accommodation etc. There are probably too many guides to the GR's, most of them useless at best so I won't make any recommendations. Each local association publishes their own guide. Thank the gods for the internet.

If you set out with an approved Credencial (available from Ivar's store (plug)) and obtain stamps from churches, hotels, bars and town halls along your route you will have a document that would support an application for a certificate of distance. AS Bradypus says you only need to evidence the last 100k into Santiago to obtain a Compostella.

Happy planning