It’s possible, but it depends on the person and the routine. It is commonly advised to go for length first. You don’t have to worry about losing girth from gaining length or vice versa, penis is not a rubber band. :)
Stretching and clamping is probably not a good idea because clamping is very intensive and makes the tissue tough so stretching would soon become futile. That’s why it’s good idea to go for length before girth.