Currently the only way is to “scrub” on the progress bar in the top right (image in this post). It’s jumpy and not super smooth scrubbing.
According to this reply, RAW data (maybe referring to PXB files?) are too heavy to scrub smoothly in camera, so might be a hardware limitation. They’re looking into the possibility of in-camera proxies that would allow for better playback and scrubbing straight from camera.
As you note, being able to scrub via the scroll wheel would be nice, especially since the current touchscreen bar is super small and would be hard to control accurately.