  Elastic systems that are spatially heterogeneous in their mechanical response
pose special challenges for molecular simulations. Standard methods for
sampling thermal fluctuations of a system's size and shape proceed through a
series of homogeneous deformations, whose magnitudes can be severely restricted
by its stiffest parts. Here we present a Monte Carlo algorithm designed to
circumvent this difficulty, which can be prohibitive in many systems of modern
interest. By deforming randomly selected subvolumes alone, it naturally
distributes the amplitude of spontaneous elastic fluctuations according to
intrinsic heterogeneity. We describe in detail implementations of such "slice
moves" that are consistent with detailed balance. Their practical application
is illustrated for a random network of cross-linked polymers.
