  We show how to place constraints on cluster physics by stacking the weak
lensing signals from multiple clusters found through the Sunyaev-Zeldovich (SZ)
effect. For a survey that covers about 200 sq. deg. both in SZ and weak lensing
observations, the slope and amplitude of the mass vs. SZ luminosity relation
can be measured with few percent error for clusters at z~0.5. This can be used
to constrain cluster physics, such as the nature of feedback. For example, we
can distinguish a pre-heated model from a model with a decreased accretion rate
at more than 5sigma. The power to discriminate among different
non-gravitational processes in the ICM becomes even stronger if we use the
central Compton parameter y_0, which could allow one to distinguish between
models with pre-heating, SN feedback and AGN feedback, for example, at more
than 5sigma. Measurement of these scaling relations as a function of redshift
makes it possible to directly observe e.g., the evolution of the hot gas in
clusters. With this approach the mass-L_SZ relation can be calibrated and its
uncertainties can be quantified, leading to a more robust determination of
cosmological parameters from clusters surveys. The mass-L_SZ relation
calibrated in this way from a small area of the sky can be used to determine
masses of SZ clusters from very large SZ-only surveys and is nicely
complementary to other techniques proposed in the literature.
