Johne,
I would think the frame rigidity comes from the whole windshield frame mounting to the helm and then the center section area where the two come together.
I'm not sure how the wiper motor would add support but I believe that is what the hole on the operator side supports. I don't know if you could also get a wiper (from the factory) for the other side but the hole looks about the same.
It may be the PO in removing the wiper, damaged the frame and I notice that there appears to be a seperation along the top frame (wiring exposed) that may have loosened it up further.
You might try and "bridge" the two peices of glass along that top frame with some aluminum stock to add some ridigity.
If all else fails, a frame to helm support (ie a DC) may be your best choice.
http://www.classicaquasport.com/gallery/showphoto.php/photo/2862/sort/1/cat/574/page/1Good luck and let us know it works out.