How to approach learning long complex piano scores without the instrument? I use musical analysis, pattern recognition, hearing to midi slowed, rewriting difficult passages, playing parts on guitar instead of piano, but still it is not fast to remember the long score precise enough to play like a pro. Mechanistic memory is most reliable and unsubstitutable, however I want to remember scores from a one or two reading attempts. Are there any other ideas which I don`t know? Thank you.
The great pianist Walter Gieseking advocated using visualization techniques.
One form of visualization (advocated by the pianist Walter Gieseking) is to study the score of the peice until you know it so well that you could sit down with a blank sheet of manuscript paper and write it out from memory. No simple undertaking! Gieseking even advised doing this before you ever try the piece out on your instrument, but that might be going a little too far. However, if you try doing this experiment with a simple piece like Lagrima, I think you will notice that you are seeing in your head what your fingers are doing, translating that into notes, and then writing it down. This is s sign that you are relying on muscle memory when you play a piece, and this kind of memorization is notoriously unreliable. [From Visualization, Solfege, and other "Aides Memoire"]
The problem with relying on muscle memory is that if you suddenly have a lapse of concentration you can literally lose your place. If you are visualizing the score you are "seeing" it in your mind, and can go on as if you were sight-reading. From what you said, it sounds like this is a method you haven't tried.
I can't offer a particular method, but you may find it interesting that Glenn Gould apparently could practice "mentally." I recall him saying this in an interview. Also, this Wikipedia page has some references about it. https://en.wikipedia.org/wiki/Glenn_Gould#Gould_the_pianist See the part near "It seems that Gould was able to practice mentally without access to an instrument..."
I don't know if any resources tell how Gould did this. Maybe he visualized the score, the keyboard, colors? Who knows.