It allows you to jump with other vehicles than only bikes. It can be used with every vehicle except of aircraft. Just press SHIFT. The longer you hold it the higher your vehicle will jump, but the height is restricted at approx. 22 yards (scaled to game of course). A bar will show your jump power.
While charging, press TAB to pause the charge and save the jump power (You can press TAB again to continue charging). Then release SHIFT in the right moment for jumping.
While charging, hold R, then savely release SHIFT to cancel (also works while it´s paused with TAB).
Press SHIFT while holding...
... X to make an instant middle jump.
... C to make an instant high jump.

It was quite hard for me to choose fitting keys. If some are nasty for you to use, or you know better solutions to control my new functions, don´t hesitate to suggest them 

Installation:
Copy VehicleJump.cs to \GTA San Andreas\CLEO

Versions:

v1.2 is online now!
-Added: Instant mid or high jump
-Added: Cancelling jump charge
-Added: When charging, you can save the jump power for using it in a fitting moment
-Changed: Max Jump height has been decreased a little bit (0.8 => 0.75)
-Changed: Jump Charge Speed has been increased (0.01 => 0.02)
-Fixed: Game crash when getting out of the vehicle while jump charging (The vehicle was defined as soon as the jump height was, but when you weren´t in the vehicle anymore... )
-Fixed: Jumps while in the air with boat won´t happen anymore (But it´s only insecure prevented)

v1.1
-Added: Bar that shows the jump power
-Changed: Max Jump height has been increased (0.5 => 0.8)
-Changed: Jump Charge Speed has been increased (0.005 => 0.01)
-Fixed: Car will now only jump when on ground (Which doesn´t mean you can´t already load it up - it just won´t proceed when in air)
-Fixed: Car will jump perpendicular to the ground your standing on, not straight upwards anymore

v1.0
-first release

Note:
There now will be two ways to jump with a bike 

BEFORE publishing or showing that mod anywhere, ASK me for permission please!

Find it also at:
http://www.taringa.net/posts/juegos/7788931/GTA-Sa-CLEO-MODS-Noviembre-2010.html
(Thanks to Daniking )

Have fun competing with kangaroos ;-P

Thanks to hamster98. I tried to code that earlier, but had no idea how to, then he published his version, which was poorly conceived, but on this I found out how I could realize it. Thanks ;-)