Yes, technically you're right. However, in my experience, it's rare for a snake to soak before or during a shed. In five years, I've only seen the behaviour a handful of times. Doesn't mean it doesn't happen. Mine usually take a bath in order to defecate.
You can also throw some damp paper towels in the enclosure. It will provide some humidity as well as something to coarse to rub against (another reason why i like spoghum moss).