  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.
