From another forum;
"Effectively, the B-1B has no external hardpoints for carrying stores. B-1Bs have the capability of carrying six dual external stores pylons, however only one aircraft ever actually carried them, it was only during testing, and the test load was AGM-129 cruise missile dummies. The external carriage of weapons degraded the Bone's performance and the nuclear mission was removed in 1991, so the external pylons were never fitted or used operationally.
So, in absolute theoretical terms, I think the B-1B has the physical capability of carrying external pylons. However, as a practical matter the do not. Besides the performance degradation, I've read that the aerodynamic forces on stores carried under the belly can damage them."