My advice, as in
this miles-long thread (see post #16 and later), is to write the source file as skreutzer or myself wrote above (with whatever needs to be fixed, and maybe add some ligature-breakers if necessary). And leave the niceties (ligatures, long-s if using skreutzer's version) to the font... and if the renderer doesn't support these basic (I won't call them "advanced") font features, shame on it.
It shouldn't be impossible to find a decent blackletter font with s-alternates and ligatures, and it shouldn't be too hard to make it Unicode-compatible, especially if you only want to use it for a few short fragments like them.