ok, so I looked everywhere for the answer, and it actually was in there, but was under the swDxfMappingFiles section.
"separate each string in the list by a line feed (e.g., the vbLf constant in Visual Basic)"
so if i want to publish sheets A, B, and C, I would do the following.
string SelectionList = "A\nB\nC";
Sometimes just formulating the question gives you the answer.