1.) Add 1/3 miracle grow potting soil to your bonsai coarse mix.
2.) Add a humidity tray under it
3.) Ignore the suggestion of a 'shade cloth'. Bougies love more sun than the sun puts out. FULL SUN ALWAYS ALL DAY LONG NO MATTER WHAT. If you just dont want many flowers/bracts, shade cloth away.
4.) Dry and then wet is fine for bougies. A friend gave me a trunk that was bouncing in the florida winter in his pickup truck bed for a month before he remembered to leave it here. Three weeks later just in coarse soil (no miracle grow here in florida, we dont dry that fast as you) and shooting all over.
5.) If you add sphagnum moss, chop it up finely. coffee grinder style. It wont really help you at all, though, but this is an alternative to step #1. About a fist full of fines would do. It'll blow away in the wind over a few months anyway, it's really just meant as a short term tool. Step #1 is meant to be a permanently-help-you step, instead.