Yeah, from the "following the railroad tracks" standpoint of any tightly scripted scenario, the hard bit is letting the players have to freedom to discover things on their own while steering them back to the plot as necessary.
Fortunately, there is one good railroading device that is tied into the plot -- the daily "reset". The PCs can't simply ignore the plot, as they're trapped within it.
One option, especially in the case where they're being specifically tested/punished as in the "redemption" concept, is that they don't have to discover what has happened without any clues -- they could be told before the loop begins that they are being punished for their transgressions and that to free themselves of the punsihment, they must learn the virtues of yada, yada, yada...
They'd still have to figure out what that means, of course, but at least they'd have a place to start looking. Our friendly BBGG might let them know from time to time if they're on the right track or not, possibly through the occasional anonymous note left where the PCs are likely to go.
I agree -- "filler" encounters (I use the term filler loosely here, as they should be more or less intended as obstacles to overcome, but not necessarily by force) should be able to be bypassed with little use of resources once they're discovered to be red herrings.