In my opinion, the BEST way to do this is to walk out of the airport in Madrid and onto a bus to Pamplona. Spend one or two nights in Pamplona, seeing the wonderful sights of the city and resting from the jet lag. Then grab a €20 bus to SJPP. Spend TWO nights there, walking to Orisson the first day then to Roncesvalles the second day.
When the rest of the pilgrims are walking
Brierley's stages and stopping in Pamplona, you'll have already seen it. You can stop before or after and get "between the wave" of pilgrims.
You can find the bus schedule from the T4Madrid on
www.movelia.es which will show all the buses leaving. I do know both CONDA and ALSA have buses going that route, so you can also check their websites.