Considering the CF May 2025, but start with a taste of the VP/Le Puy?

Why not consider starting in Lourdes? Quite easy to get to, and an interesting destination in itself. Probably about 150 kms from SJPP.

Another town along the VP about 5 - 7 days from SJPP is Pomps. You would have to research how to get there by public transport. It's pretty small. There is one tough stage just after Landaco, to the Chapelle de Soyarce, up a hill of about 2 kilometers, and a magnificent view at the top.

With regards to the Le Puy route...

Here is an option that I did with my sisters two years ago, that adds three days to the Camino Frances...

Day 1: Navarrenx.

Start in this lovely walled city on the Le Puy route (GR65).

Day 2: Saint-Palais.

Saint-Palais is on a variant of the GR65, and is a gorgeous town. It's a bit of a walk to get there, so we walked to the Gite in Aroue and the owners there helped us call a cab to Saint-Palais. It's about a 5-10 minute ride. Aroue is just a little village with virtual nothing in it. (The Ciccerone book is good at showing the variant route to Saint-Palais, if you want to scope it out.)

Day 3: Ostabat-Asme or Larceveau.

If you leave from Saint-Palais, there are two large hills on this stage. It's a nice warm up for the Pyrenees. This is one of my favorite stages on the Le Puy route. Lovely views all day.

Day 3: Saint-Jean-Pied-de-Port.

A pleasant walk, and quite a shock as you go from a quiet trail with no one on it, to a town full of pilgrims. A beautiful city though. I've been here twice, and loved it both times.

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If you want a longer walk than this, you could start a few days earlier on the trail in Arthez-de-Béarn, Arzacq-Arraziguet or Aire-sur-l'Adour (or something in between), but none of those towns stand out as anything special to me.

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FWIW... The first 10 days out of Le Puy are really nice. If you walk those, you would love it, but it would be a full day of train/bus rides to get to SJPDP when you're ready to jump ahead.