Looking for options for reversed Camino

Hello! My title for my query is a. It misleading but I could not think of another way to word it! I am working on a different kind of itinerary for my Camino del Norte next summer. Rather than start in Irun, I wish to start in Bilbao, walk west to Vilalba, then bus back east to Irun to walk back to Bilbao. I’ve read that the first seven days (Irun-Bilbao) are the hardest and most beautiful of the Norte. I don’t have great knees or ankles and I thought that keeping the Irun-Bilbao segments for last would enable me to toughen my joints and feet and optimize my chances of not injuring myself. My challenge is how to get my bag transported from Vilalba to Irun as I have not found a company that does the transfer in that direction. Has anyone done something similar for an itinerary and was successful in finding a company to send their bag east instead of west? I’ve emailed Correos but was not able to get an answer from them.

The need to have the bag transported is also related to my arthritic knees and bad ankles.

Thank you!