Not trying to change your course of action..well actually maybe I am, but have you tried rooting in coco coir?
I have done an even split this year, every variety has been divided into 2 different bags. One with quality LFSM and one with coir. So far, things have been fairly even between the two groups. I'm not talking huge numbers of cuttings here, but the data is good none the less. 3 different varieties, 4 cuttings of each variety. The sphag have rooted 4 out of 6, with 4 in cups growing, one still taking it's time in the bag, and one which started to grow shoots and was callused, but no roots, and eventually failed; at least that is how it's looking, I'll let it hang in the cup for another couple weeks before I dump it. The coir are 6 for 6, all rooted and growing in cups.
I have another 4 cuttings I started about a month later(~2 wks ago), same scenario, I just cupped the first one from the coir bag yesterday. I also started 3 of a different variety last week, and I put all of those in coir. I have to say, I am..or was a LFSM guy, but coir is more available, I haven't had any mold with it, it is so simple to cup the cutting(meaning no issues with the root tangle or breakage what-so-ever), and I can add the coir I used for rooting to the cup mix or later down the road for the potting mix. Long fiber sphagnum, while it can be sterilized in the microwave or boiled and reused again, I just prefer not to, and since I don't add it to the potting mix it's usefulness is done there. I totally agree about using the quality moss though, my first choice is the Angel Moss from New Zealand, it's premium with no mold issues. I have heard the company that used to supply it is no more, and I have bought it whenever I come across it. Luckily, thanks to FMD posting about his luck with coir I decided to give it a test run and now I don't have to worry about hunting down Angel LFSM again.
I prep the coir the same way I prep the LFSM, put the dry product in a cup with some warm/hot water and let it set for 10-30 minutes and then strain it out with my hand and squeeze every drop of water I can out. Lay the cuttings on bed of coir and then cover with more coir.