I've recently begun practicing score reading AFK. But with pieces that I'm familiar with (I know the music, but have never tried playing it on piano). When I try to hear an unfamiliar piece in my minds ear, what I get is an approximation - it's very vague, uncertain. I'm not sure whether this practice will develop that ability, but I have a hunch it will over time naturally progress into it.
Even if not, I've been finding score-reading to be difficult for me (and rewarding!). My basic approach is to memorize the notes from the page, one-by-one, then short motifs, then phrases. Also visualizing the notes/motifs/phrases as keys on the keyboard, then visualizing a fingering and imagining my hands playing it (HS, I haven't figured out how to visualize HT yet). At that point, it begins to feel real to me. My goal is to fill in every detail I can think of in my head, after I have it all memorized I plan to begin playing around with interpretation.
I've been working on a simple piece so far, and don't want to take it to the piano until I'm all done AFK... I can't say anything about the results yet.