OBJ format has the facility to specify seperate objects within one file ("o" lines) which Blender will write when the correct group option is chosen when exporting ("Object Groups").

The problem of course is that Poser's importer ignores these and treats the whole file as one object.
The best solution would be to have Poser process the file with a script that creates the appropriate number of individual props rather than exporting multiple OBJs.