Yeah, the most realistic (but still extremely unrealistic) way of achieving it would be a constitutional convention.

Besides it beingunrealisticto even make it happen, that would be a horrible idea though, since there being little to no framework about exactly how it would work, which means that unscrupulous politicians (*cough& Republicans cough) could potentially add or remove several other amendments.

All that to say that this is probably the most effective method currently available. As a bonus, the SCOTUS overruling it would probably cause such an uproar that Congress would attempt to introduce a new way that CAN'T be blocked but doesn't require changing the constitution.