Right click the morph parameter you want to split. Sometimes you may need to save and refresh Poser to get the command to appear. The command will split the morph into 2 dials, left and right sides, and leave the original whole intact. Note; be careful if you decide to delete a freshly created split morph dial, this will promptly crash Poser. If however you've saved and refreshed the file after the split you can delete as usual...