Tinkerer, shminkerer. Knock yourself out, and I really do wish you the best, but I would be shocked if you can do this in an attractive and professional manner. If it makes you happy to think you will arrive at a good looking and working product like one off the shelf should be, more power to you. But I don't see how it is possible to chop up a saddle and have it pass for an off the shelf item. Cutting through the nylon shell after a saddle is completely assembled is no easy feat. Doing it neatly and symmetrically is nearly impossible. I really don't think it is about what glue you use. The key to obtaining a cut out saddle that you like is to transfer the characteristics of your current favorite regular sadded to the new one: i.e. length, width at the sit bones, padding quantity, padding density, etc. If you buy a similarly sized and designed saddle to the one you like, but with the cutout, it should come very close to being right for you. Is that how you chose the cutout saddles you already tested?

As far as the value of cutouts is concerned, I do find they are very functional for relieving stress on a sore prostate, especially when the sit bones are properly supported as well. Many folks think saddles are all about looks, but they have to be designed just like you are to work as they should. My favorite, the Terry Falcon Y with a generous cutout, is a little wider at the back than the standard racing saddle without being heavier or "dumpier". For me it is perfect. YMMV.

Bona fortuna!