Davebugg (above) accurately cites the actual language from the Cathedral's web page. Catholic doctrine also holds that a live person can obtain the indulgence for a deceased person, by performing those specified sacramental actions, read above... The attribution and accreditation is entirely spiritual...
Also, it should be noted that the conditions set out by the Church for obtaining a plenary indulgence DO NOT include a pilgrimage. However, many pilgrims do combine both. Hence, it is possible to drive, or ride into Santiago and perform the specified actions to obtain an indulgence.
Regardless of the indulgence issue, you CAN receive your Compostela annotated at the bottom "In Vicare Pro" (Latin for "in place of") followed by the name of the person you are dedicating the Camino to. This is used by a living person to dedicate their effort to the memory and soul of a deceased person, or to a living person whose physical condition means they could NEVER accomplish a Camino of their own. Just ask the staff person when you arrive at the counter. It helps if you already have the correct name of the other person's name printed out in Roman letters.
Doing both the sacramental actions to obtain a plenary indulgence and the In Vicare Pro annotation should be adequate to purpose. There is NO certificate to indicate you have received an indulgence.
The practice of issuing formal, written indulgences, typically in exchange for some payment, created a huge scandal in the 1400 and 1500s and is one of the many issues Martin Luther cited (correctly) in his "Ninety-Five Theses" document of 1517, and his subsequent split with the Catholic Church. This practice has LONG since been abandoned. So, obtaining any indulgence is strictly a spiritual thing...and is FREE...
Let's face it, no one shows up at the Pearly Gates waving a Compostela or other paper document proclaiming their entitlement to enter. If we are to believe our Christian faith(s) [plural] the BIG BOSS knows all...
Hope this helps to clarify...