You should be able to just iterate over a feature set and push the items into the GPX file.
Thanks Mike for the link. I think it can do what I wanted to do... However, we decided to take advantage of ArcGIS Online to share our mobile data if required instead of exporting to GPX or shapefiles. We'll be looking at authorising a web map on ArcGIS Online that has access to our arcgis server mobile feature services. Then from within the iDevices we just simply email the link to the web map with the bounding box coordinates or centroid of the map view...