Actually, that is a simple one.

Export wavefront obj file.
In your export select all of the props. => Poser will save them out as a single obj file.

Goto Blender, mirror, export as obj file.
Open Poser, import mirored obj file.

Poser 1, 2, 3, 4, 5, 7, P8 and PPro2010, P9 and PP2012, P10 and PP2014 Game Dev
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