They meet over Skype and share their documents through Google Docs accounts. They are able to have the same types of conversations as they would face to face, and be able to look at the same documents with ease.
Here are some articles for schools that may be struggling to put together PLC teams with singleton teachers. Two excellent leaders in this area!
There are many ways out there for small schools or elective teachers to participate in the PLC. We have to find ways to be creative to make it work. I encourage you to work with other schools to create partnerships, it will be extremely beneficial and singletons will not be left on the outside looking in.