There is bus service to most villages. I don't know if they will stop to pick up flags between scheduled stops.
Once you get past Astorga most of the camino is located away from roads wide enough for buses. If there is service its once per day at most and some places have no bus service at all. Otherwise you have to go from one village to another via a transport hub such as Lugo.
Transportation Hubs
Pamplona
La nueva estación de autobuses de Pamplona está construida con el objetivo de acercar lo ultimo en comodidad y movilidad a sus clientes.
www.estaciondeautobusesdepamplona.com
Autocares Artieda Roncesvalles to Pamplona
La Estellesa Pamplona to Logrono
ALSA SJPdP to Pamplona (but no pickup between these stops)
Burgos
Sitio Web del Excmo. Ayuntamiento de Burgos
www.aytoburgos.es
Autobuses Jiminez Logrono to Burgos
Amaya Burgos to Fromista
ALSA Carrion de los Condes (and Osorno) to Leon
There is no direct service between Fromista and Carrion de los Condes
Renfe train Fromista to Osorno
ALSA Leon to Ponferrada
There is once per week service local bus to and from Astorga to Rabanal
There is no bus service between Rabanal and Ponferrada
ALSA Ponferrada to Piedrafita do Cebreiro (no stops)
Gonzalez y de la Riva Ponferrada to Vega de Valcarce and El Castro on demand
Empresa Portomarin (not confirmed) O Cebreiro to Sarria. If there is service its once a day each way during weekdays only.
Empresa Portomarin Sarria to Portomarin
There is not service between Portomarin and Palas de Rei.
Empresa Portomarin Portomarin to Lugo
Empresa Friere Lugo to Palas de Rei
Empresa Friere Palas de Rei to Santiago