We played it in a literal sense this past Sunday.

If the psyker was actually "hit" (aka: precision shot, closest visible model) then he took perils, even if his unit could LoS! The actual S5 wound off him. The only time the guns were used was on tyranid MC's but I feel this is a "fair" way to keep me from murdering the hell out of a librarian.

Guess you'll need to make your own FAQ if GW doesn't for railhead eh?