  A phenomenological formalism is presented in which the apparent acceleration
of the universe is generated by large-scale structure formation, thus
eliminating the coincidence and magnitude fine-tuning problems of the
Cosmological Constant in the Concordance Model, as well as potential
instability issues with dynamical Dark Energy. The observed acceleration
results from the combined effect of innumerable local perturbations, due to
individually virialized systems, overlapping together in a
smoothly-inhomogeneous adjustment of the FRW metric, in a process governed by
the causal flow of inhomogeneity information outward from each clumped system.
We discuss several arguments from the literature claiming to place sharp limits
upon the strength of backreaction-related effects, and show why such arguments
are not applicable in a physically realistic cosmological analysis. A selection
of simply-parameterized models are presented, including several which are
capable of fitting the luminosity distance data from Type Ia supernovae
essentially as well as the best-fit flat $\Lambda$CDM model, without resort to
Dark Energy, any modification to gravity, or a local void. Simultaneously,
these models can reproduce measured cosmological parameters such as the age of
the universe, the matter density required for spatial flatness, the present-day
deceleration parameter, and the angular scale of the Cosmic Microwave
Background to within a reasonable proximity of their Concordance values. We
conclude by considering potential observational signatures for distinguishing
this cosmological formalism from $\Lambda$CDM or Dark Energy, as well as the
possible long-term fate of such a universe with ever-spreading spheres of
influence for its increasingly superposed perturbations.
