The Brazilian manufacturer revealed the plan at the Paris Air Show only a day after Kawasaki announced ongoing studies to convert a baseline C-2 military transport into a commercial freighter.
The KC-390 is being developed for $1.3 billion by the Brazilian Air Force to receive military certification in 2016. A stretched model could be available as early as 2018 for the commercial transport market, which includes Brazil's Correios postal service - the original launch customer for an earlier version of the KC-390.
The civil version would have to be modified with two plugs added to the 33.91m (111.3ft) length of the KC-390's fuselage, Orlando Neto, vice president of sales for Embraer Defence and Security, said in an interview.
One plug would be added forward of the wing to accommodate a side door for cargo. Another plug would be inserted into the fuselage aft of the wing to create more internal space, Neto said.
The existing wings and engines of the KC-390 are sized to accommodate the stretched version for the cargo market, he added. The KC-390 also features an avionics system - the Rockwell Collins ProLine Fusion - design to receive Part 25 civil certification in 2015.
Embraer's commercial plans for the KC-390 over-shadowed the lack of further announcements about the airlifter's supply chain.
Despite recently entering a year-long joint definition phase, Embraer has yet to finalise agreements with the engine supplier for the KC-390. Both the CFM International CFM56 and the International Aero Engines V2500 have been considered for the order.
Neto confirmed that discussions are concluded between the company and the Brazilian air force over the engine supplier. The discussions are now between the company and the suppliers, although declined to clarify if one of the companies had already been ruled out.
But the discussions are also not expected to drag on indefinitely. Neto added that Embraer has a firm schedule for completing the negotiations, and a contract award is possible within a few weeks.