How can I jump really high in Mario Kart 64?

Some levels, such as Toad's turn pike and the train level, have big shortcuts if you can jump over a large wall.

How can I jump over walls in Mario Kart 64?

Update: the rainbow road jump does not count since it can only be done in a specific place and this is due to the map containing a huge down hill part in the level.

You can use other drivers as "spring". That at least worked for when starting a race from last position - pushing A just in time for a speed start, then pushing R to jump on the driver in front of me, which causes my to bounce in front of the field. I guess this can also be achieved with a mushroom when another driver is in a good position.

One way I have figured out to do this is to be someone fairly light weight (e.g. Toad or Yoshi), then get a buddy to play as a heavy-weight (e.g. Donkey Kong). Next, have them line up right near the wall, facing towards it. Now you will need a mushroom and to line up behind them. Once you are lined up, you stand a little behind them such that the mushroom will give you enough power to run into them, normally causing your character to spin out. Right as you hit them, though, press the R button to jump. If timed correctly, this will launch you fairly high up, enough to jump over most walls.

If you time it correctly, you might even be able to do this without organizing with a buddy, since this does work while the heavy-weight is driving. It just might be really hard to line up correctly while both of you are driving.

I don't know about those two shortcuts, but the shortcut in Wario Stadium requires you to hop just as you hit the wall. When you time it correctly, you can jump up and over the wall.

Here is a video showing the Wario Stadium shortcut.

This video shows a number of different glitch / shortcuts. Toad's Turnpike is at 3:49, but it appears to be more of a glitch with the texture seams than an actual jump over the wall.