It might (with a strong and healthy emphasis on the word “might”) be possible to thread a cosmic string through a wormhole, and let it loop back on itself through normal nonwormhole space. Closed cosmic strings vibrate like your hands after your fourth shot of espresso, and those wiggles might just have the right interaction with spacetime to make the local energy dip into the red, providing the necessary stability. At least, until the cosmic string vibrates itself into oblivion through the emission of copious gravitational waves.
