Well, not sure what's the "best" way to do it, but I faced a similar situation when I decided to add an elevated loop of track to my already built 8 X 8 layout. All of my other track was O-27, so I extended that to the el loop, and supported it on eighth-inch thick hardboard over supports made of dowels and strips of wood. I fabricated extra wooden 'ties' to fit in between the OEM metal ones, and added splines of hardboard underneath the spans, to add some additional rigidity, and fabricated some fences along the curves to inhibit any mishaps! Here's a few pics:
And here's the el in operation:
