Light blocking and reflection can be useful for avoiding adding lights. Placing tall cubes around the subject and a flat plane underneath out of camera shot will allow the HDRI lighting level to be increased slightly but retain contrast, these blocking primitives need to an appropriate shader for the surroundings as it will be reflected back onto the subject. Adding a primitive with a lighter colour can act like a fill in flash. This approach is more useful for outdoor renders where 90% of illumination is reflected lighted from a single source. The effectiveness of this approach varies depending on the HDRI map.