Here's a fringe idea in the worse case: Connect one ECMO oxygenator to multiple patients at once using Type-O negative blood. You'd have to filter out the O-negative RBC's as they come in.
Not only does transfusion present a big risk, we quote ~20% risk of adverse events (minor to severe), but what you’re suggesting massive transfusion protocol (DIC, hemolysis, TRALI, TACO) AND ECMO which itself is orders of magnitude more dangerous than ventilation.
The risks are numerous but for brevity sake you have: Acute limb ischemia, DIC/other coagulopathies and spontaneous hemorrhage which carry huge mortality.
It would be way simpler and safer to connect multiple patients to the same ventilator who are all on CMV with similar settings.
ECMO is not saving many people with severe COVID-19 related illness. It depends on buying time for your body to recover. Nearly every case I’ve read about that required ECMO the patient died because of multiorgan failure and sepsis. ECMO only works well in patients with isolated lung (and some circumstances heart) problems.
Even if you manage to double or triple capacity unfortunately it is no match to the exponential growth.