We study wormhole contributions to the bulk path integral in holographic models which are dual to ensembles of rational free boson conformal field theories. We focus on the path integral on a geometry connecting two toroidal boundaries, which should capture the variance of the ensemble distribution. We show that this requirement leads to a nontrivial set of constraints which generically picks out the uniform, maximum entropy, ensemble distribution. Furthermore, we show that the two-boundary path integral should receive contributions from `exotic' wormholes, which arise from the inclusion of topological surface defects.
Comment: 35 pages, 3 figures. V2 minor corrections, references added, published version