First, that's not flight, that's gliding.
Without some mechanism to generate lift, i.e. by flapping, flight by the use of rib extensions is basically impossible. They can be extended, but in Draco the wings are fixed.
However, you can possibly develop some form of "false" ribs, by employing a novel joint above the ribcage, perhaps attached by cartilage and ligaments to lengthened neural spines. This would allow you to anchor "pull-up" muscles to the longer neural spines. To get around needing deep breastbones for the chest to anchor muscles to pull the wings down (take a look at a pigeon skeleton, their keels are huge relatively speaking), they could have anatomy that automatically forces the rib-wing, once extended to want to fold forwards (have the tips meet in front of the creature) so that the major force would be from the spinal process muscles pulling the wings back and open and anatomy pulling them closed. Sort of like a clap, where the effort is in you drawing your hands back, not in bringing them together.
Also, unless the creature is very short-legged, I don't think you're going to have enough body length, even if you took the rib wings from behind the shoulders to the hip to give you an adequate wing to mass ratio for flight or gliding, a human torso is too short to fit a wing that can support the heavy head and legs, the legs make the whole thing too back-heavy.
If you are okay with "rib_like_" structures, you might be better off attaching the extensions to be above the spine themselves. They can still use the neural spines to anchor muscle, but the down-stroke force would have to be generated by muscles pulling the ribs downwards. And you end up with a flier kind of like this:
Versus a regular six-limbed sort of flap (it's big so I didn't past it in). https://i.stack.imgur.com/bumiN.jpg
But again, note how much length is given up to be a continuous wing to let rib-like projections work. I think this version is much more anatomically feasible than the first option, fitting the rib sails directly above the ribs to the sides of the spinal process. Though you might end up with a humanoid creature that is built very deep and broad of chest, with a buffalo hump. They would be humanoid but not humanlike in shape.
The "buffalo hump" need not stand out. Buffalo have their hump because their neural spines are tall to support the weight of their heads. You can see the same with rhinos, which do not look particularly humpy, but have tall neural spines as well.