While trying to add player's speed as a drug effect, I realized that player.Speed only works when a player is not colliding against anything. It only works when a player is in mid-air. As soon as you touch the ground(or any other collision), the speed changes to default as per GTA:VC physics.
Speedhacks did not become a reality, but here is a snippet that makes the player jump higher. This is very inconsistent in a crowded server due to performance issues, but the code and the idea can be implemented.
Code
Pastebin (http://pastebin.com/SxdcdFUY)
Usage
To enable a player's longjump, create an instance of the CLongjump class. Parameter: player instance.
Example:
function onPlayerSpawn( player )
{
local pLongjump = CLongjump( player );
}