This communication reports a strategy for scale-up of an in situ polymerization technique for polyolefin-based nanocomposites preparation, taking layered silicate (clay) and multi-walled carbon nanotubes (MWCNTs) as examples of nanofillers. The strategy is realized by transforming the nanofillers into granular "nanosupports'' for Ziegler-Natta catalysts. With a catalyst to polymer replication effect on particle morphology, the in situ prepared nanocomposites are of controlled granular particle morphology. With the polymer particle morphology controlled, the in situ polymerization technique becomes suitable for industrial olefin polymerization processes for mass production of polyolefin nanocomposites.