I had a lengthy conversation with Geoffrey Landis about exactly this several years back. We haven't ruled out the possibility, but we also theorize that the amount of energy necessary to expand the radius of the singularity beyond "singularity" is of the "consuming stars" variety and that differences in angular momentum between the ends creates energy deficits of a similar magnitude. Yeah, if you can mold black holes like Play-Doh you get to mess around with wormholes. If you don't even know how to contain one, spaghettification.
It's like Dyson Spheres - yeah, theoretically you could do that. Practically, when the denominator of your equation includes "neutron star material" the theory remains theoretical.