Practice tips and warming up

This is a meandering post about these two points, so I apologize for it being compositionally incoherent.

I found a wonderful list of practice tips here:

Practice tips
It's odd how I know all of these things, as I'm sure most trained musicians do, but when I'm in the heat of practicing it's hard to remember. I'm posting it here in case any readers are in the same boat. (NB: The link doesn't always work, but keep trying; it's worth it.)

The best one -- and one we all need to remember -- is not to practice faster than you can comfortably play perfectly. This is one of the hardest for me. I have been panicking ever since I heard what Pezzo Capriccioso sounds like when played too slowly that I won't be able to play it fast enough, and I've been trying to prepare by practicing it fast, which I am doing too much, I know. OTOH, once I warm up I can play it much faster than when I try to play it cold.

Related to this, I'm finding that I simply cannot play the 32nd-note passages up to tempo before I warm up and practice them slowly for about 45 minutes. I started worrying about this because I was thinking about the logistics of the concert in June and realized that there is no backstage at all in this church. The space where we used to play was also a church, but it was a huge old building with a rabbit warren of rooms and hallways behind the altar where you could warm up in complete privacy. Here, there's a little space off to the side of the altar that is in full view of the audience and that's it. There are a couple of small rooms at the back of the altar, but we really aren't supposed to use them.

I'm pretty sure I'll be playing immediately after intermission, so I guess I'll just have to practice thoroughly before the concert and then sit off to the side and noodle as best I can before the second half.

The link above doesn't have any really helpful suggestions for this problem, but I also found a discussion here by pianists about this very issue:

Performing without warming up

Pianists have to deal with this all the time because they can't touch their instrument until they walk out on stage.

The following suggestion was intriguing, and I will try it this evening and report back:

The Percy Grainger warmup: sit down in any regular, straight-back chair. Smack your knees with your hands, repeatedly, hard and fast, for 5 minutes. If it doesn't hurt you're not doing it hard enough. It's actually quite hard to keep going for 5 minutes but it certainly gets the blood flowing.

(Seems like you could end up with bruised knees, though.)