You neglect to indicate the format of export, or where you are going. You might draw on what the python source for MHX2 does as a starting point.
If you do not mind doing it post export, another starting point is the client server method. That goes from MH the server, to a Blender pose library. I believe the server is already inside MH for 1.1.1, right joel? The repo is here.
https://github.com/makehumancommunity/community-plugins/tree/master/blender_source/MH_Community . If you do not specify an expression tag to filter by, then it transfers all expression loaded. this is in contrast to MHX, which only the standard expressions on the export file.