Well this turned out to be a fairly simple process. The rocker part of the switch is just a cover, which with a bit of gentle effort pulls off, leaving the bulbs visible. The only tricky part is pulling out the tiny capless bulbs with out breaking them. They are too far recessed to get a hold of, so a small pair of pincer nosed plyers is the only solution. A little double sided tape wrapped around the end of the plyers helps to get a good hold without exerting too much pressure.
