Basically title.

To do it, bind Jump to a MWheel direction (I used MWheel Up since my MWheel Down is bound to Crouch for Floor Clipping), then sprint, jump, hold Crouch while in the air, and use your MWheel Jump as you get close to the ground to bounce.

If you have speedrun Half-Life 2, this will feel very similar to the input needed for Accelerated Back-Hopping.

You MUST have Crouch set to Hold and not Toggle for this to work. If you have Crouch set to Toggle, you'll just stand up as soon as you jump. I also found I was no longer able to Floor Clip with Toggle Crouch, so you probably don't want to use it, anyway.

Also, you CAN preserve momentum by jumping as soon as you hit the ground. I confirmed this in the on-foot sequence near the story end. The Jump-Pad-like things that launch you from one section to the next move you at higher speeds than just sprinting. By crouching and using MWheel Jump you can preserve this momentum. With this being the case, it might be possible to build up speed using airstrafe or similar tech.

I do feel I need to note that keeping this going feels really tricky compared to other games with similar movement tech - like ABH/ASH in HL2 - particularly when trying to move uphill, even just slight slopes. It's possible this is just a skill issue, though, and I'll keep practicing it.

It is also possible to scroll too quickly and you end up just jittering and losing speed. I have a Logitech G903 mouse that allows you to unlock the mousewheel and let it spin freely. Trying to just unlock the wheel and spin it rapidly resulted in the jittering I mentioned.