Poser itself can do welding on the fly, no need for the vertices to be welded in the obj file. The figure section of the cr2 should already contain statements to weld the abdomen and thighs to the hip, eg:

    weld abdomen:1
    hip:1

    weld rThigh:1
    hip:1

    weld lThigh:1
    hip:1

However as nruddock said "The vertices on the group boundaries would have to match exactly for welding to work".