I often practice on pieces i'm working on. Like if i want to try a new or different finish on a pen blank, i'll round it and go through the new finishing steps well before i've turned to the final diameter. Then that new process can be turned away, often with enough material to try it again. In the case of your bottle stopper, maybe cut the blank 1/2" to 1" longer than your desired length, and work on the top beads a few times--a little wasted material, but better than losing the whole blank if it doesn't work well on the first try.
earl