Interesting, I've always used my middle finger for the scroll wheel.

For scrolling small distances there's the mouse wheel; for everything else there's spacebar.

I have a button on my mouse to make the scroll thingy freewheel, it's pretty neat.

Don't forget the venerable arrow keys

I just put a rock on top of Page Down.

I wonder whether there's a market for "key weights" that fit a key exactly and are heavy enough to keep it pressed. Depending on the occasion I have used heavy implements (not exactly rocks), a variety of wedge-like tools like scissors and other things to keep a key pressed, but a dedicated tool such as a properly-shaped paperweight might have been much nicer ;)

In linux you could write a script with xdotool to select the window you want and spam whatever key/sequence of keys you would like.

this kind of interface is totally made for a touchpad or touch screen. on anything else, it's weird. or even weirder, anyway.

Click the middle mouse button. Move the mouse down slightly. The more you move it down, the faster it scrolls.

No need to hold any buttons.