With rising fuel prices and increasing environmental pollution, attention has turned to renewable, biodegradable alternatives to petroleum-based plastics – specifically bacterially synthesized polyhydroxyalkanoates. Previously, a novel genetic pathway was described using fragments from the bacterium Ralstonia eutropha and Clostridium kluyveri that allowed for the production of poly(3-hydroxybutyrate-co-4-hydroxybuyrate. Here, we describe and characterize a modified version of that pathway that allows for the strong regulation of the resulting co-polymer composition through the use of the tetR and lac promoters. The separate regulation of key genes for the two separate pathways (phaA, phaB for 3HB and cat2 for 4HB) allows us to fine-tune polymer properties through the addition of extra-cellular isopropyl β-D-1-thiogalactopyranoside (IPTG) and anhydrotetracycline (aTc). A key goal is the maximization of the 4-hydroxybutyrate percent composition, as this monomer confers desirable elastic properties to the resulting polymer. This system will allow for high-throughput commercial production of custom-tailored polymers where the previously described method of substrate switching is not feasible.