I wonder how one learns such pieces within the time and limitations stipulated by the OP and more or less performance ready (except for the tempo maybe) if one cannot even sightread the material at moderate tempo. Not being able to sightread a piece is clearly a sign that a person is not actually ready for it, so he/she has to put lots of time into compensating for what should have been there in the first place.
You infer what I did not mean to say. I said that you have to know the composer's idiom to be able to sightread the piece. I may be mistaken, of course, but I suspect that if one can't sightread a piece at moderate tempo, then one is either not familiar with the composer's idiom, or one has a poor command over the keyboard. Reading the notes is not the problem; it's shaping the notes musically the first time around that is the challenge.
The learning itself may not be a punishment. The ordeal comes when the highly critical teacher who tells you to do the task within X days is disgusted with how you perform. As in: "bring me Liszt's Orage in three days" and in three days, you play everything right except for the octaves. As soon as you have been through such an ordeal, it becomes part of your practice regimen to avoid that kind of dreadful experiences. I can assure you that that is not so much fun sometimes. 
Ooooh I just remembered! One time I was browsing YouTube and I saw some guy performing a piece in 11 staves. I don't remember whether or not it's an easy piece, but 11 staves? Nobody can sightread 11 staves. But he still perfromed it.
So then I guess that I'm not ready for something like fur elise.
What if you end up learning something without being able to sightread it? (all of my repertoire) does that still mean that I'm not ready for it? I mean, I can play it fine, and if I hadn't told you that I wasn't able to sightread it, you probably would've thought, 'ah, he does a pretty good job' (just for the sake of argument). I wouldn't say anyone's not ready to play anything unless a week passes by and they're still on the first page or something. THAT'S a brick wall.
Ah, I see what you're saying. I'm pretty familiar with Rachmaninoff, but I still can't sightread his stuff. But because I've played his stuff before, I'll learn his music faster than I did my first time learning his stuff. You can be familiar with a composers idiom but still suck at sightreading. And it doesn't mean that I have a poor command over the keyboard. I can barely read (not even) Mozart sonata No. 16 but I know for a fact that I can play it just fine. Unless you mean something else when you say command over the keyboard.
ahaaaa I think when you say 'if you can't sightread something then you're not ready for it', I really think you mean that you're not ready to learn it in a
short amount of time? Which you actually CAN do, it just takes a bunch of practice.
Just because you can't sightread doesn't mean you don't know what's going on. Lets say you're doing something it and you spend a while learning the first half of it, then you get to the second half, and most of it is the SAME THING but in a different key! So instead of learning 10 pages, you're only really learning five. So you spend a little bit of time figuring out some finger work and stuff. Not being able to sightread something well doesn't mean that you hit a brick wall. You kinda feel you way through the piece, and you find patterns and as you move forward it gets easier. And if you're familiar with the composer, it makes it even easier! It's not like you're stuck on the first page for like 30 days or something.
Topic: Learning a Mozart Sonata in 7 days