I just realized how difficult getting a score-only soundtrack may be. There are a few instances in the soundtrack that have dialogue over the score. Unless there is some bootleg release out there that has the dialogue omitted I wouldn't know how to remove it without noticeably effecting the audio quality.

For example, when Deckard enters Tyrell's office Rachel greets him, "Do you like our owl?" and that conversation is present in all of the score/soundtrack releases I've heard. I believe it occurs in other instances of the score as well where you can hear background noise and dialogue from the film.

In any case, if this were to be accomplished it would also mean getting a complete, no dialogue cut of the film score and that would be another first!