I bought a platycodon and want to chop the top third off (I would have done it earlier if I grew it myself). The wind will probably snap the stems anyway but I'll lose the first buds.
I wondered if I could put them in water or something to grow roots. Once I accidentally cut the stem of a morning glory, and put it in water, and the plant grew roots and survived! I was hoping the same might work for the tops of the balloon flower.
It's a shame to just throw all of that growth away.
I don't know how well it will work with this plant but its worth a try. I've had great luck doing it the way you mentioned with other palnts but I've had equally the same amount of failures.
Keep it in a bright location out of direct sunlight and let us know how it works out.
I just cut about a foot off the tallest spikes, made them into 6 cuttings, took all but the top leaves off each. Cut the buds off so energy doesn't go to them. Put them in tap water in washed yogurt tubs and placed on window sil with a translucent material in front of the window so direct sun will be partially filtered.
I also did some leaf cuttings in chevron shapes and pushed them into some moist soil.
I'm going to expect 100% failure rate and not invest any hope into it. They would have gone in the garbage anyway.