You set the focus, or rather magnification and then move the lens till the subject is in focus. That’s what I do with my MP-E and I don’t drug or cool any of the jumping spiders I takes pictures of.
Then all you need is a microscope objective, or a whole microscope. Personally, I have a Zeiss Stemi DV-4 Stereomicroscope and a basic Fisher compound microscope for personal use, with adapters to fit an EF mount to the eyepiece. The Zeiss Stemi is a fun little scope that goes up to 32x.
I shot in Europe here and there some zebra jumping spiders with my EF 100mm Macro and extension rings with AF, but I had to act really fast. There is a short moment when they seem to be stunned by the reflection in the lens, I guess it could be the mirror image of themselves, but that's usually a not much longer than a second. I keep your technique in mind, when I buy an MP-E (I were several times very close to hit the buy button). With a fast fps burst it should be possible to get keeper images more easily.
