On the Violaman site there was an old post. In that post Violaman (aka Fiddlerman) provided a video of a luthier showing you how to put purfling in a violin, I would assume the same process would be used for a viola and cello.
Hey, Fiddlerman, I hope you don't mind that I used Violaman's link.
This was from an old post where someone who was given a violin in need of repair. After he decided he liked the sound of a viola better, he decided to repair the violin. It was a neat post. I saw Violaman's reply and he included the above video. I thiught I would share this video here.