Hi Dalachin - I think a combo of humidity, moderate light, and patience are your best best. Sounds like you are doing most of this already - i might soak the jongheana directly in a kelpak solution for 24 hrs instead of sphag at the rhizome for more direct application. I did that almost 2 years ago for a few divisions, and they began rooting a few weeks after that.
Keith Davis will give rootless divisions the "sphag and bag" treatment and place them under his growing benches and he has great success.
Good luck! It's such a relief once roots and new growth start.
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David
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