I germinated them floating in pure water. Substrate is Chilean long fibre sphagnum moss and perlite, I don't remember the ratio. 50 to 75% perlite most likely. I don't recall who recommended the mix, perhaps Pyro or it just seemed right to me.
Don't fret. The U. alpina seed I got from Pyro took forever to sprout and then vanished seemingly overnight a few months later in the same substrate.