[Jerry]

Check out:
IGameMovement (igamemovement.h)

     //========= Copyright © 1996-2005, Valve Corporation, All rights reserved. ============//
     //
     // Purpose: 
     //
     // $Workfile:     $
     // $Date:         $
     // $NoKeywords: $
     //=============================================================================//
     
     #if !defined( IGAMEMOVEMENT_H )
     #define IGAMEMOVEMENT_H
     
     #ifdef _WIN32
     #pragma once
     #endif
     
     #include "vector.h"
     #include "interface.h"
     #include "imovehelper.h"
     #include "const.h"
     
     //-----------------------------------------------------------------------------
     // Name of the class implementing the game movement.
     //-----------------------------------------------------------------------------
     
     #define INTERFACENAME_GAMEMOVEMENT    "GameMovement001"
     
     //-----------------------------------------------------------------------------
     // Forward declarations.
     //-----------------------------------------------------------------------------
     
     class IMoveHelper;
     
     //-----------------------------------------------------------------------------
     // Purpose: Encapsulated input parameters to player movement.
     //-----------------------------------------------------------------------------
     
     class CMoveData
     {
     public:
         bool            m_bFirstRunOfFunctions;
     
         EntityHandle_t    m_nPlayerHandle;    // edict index on server, client entity handle on client
     
         int                m_nImpulseCommand;    // Impulse command issued.
         QAngle            m_vecViewAngles;    // Command view angles (local space)
         QAngle            m_vecAbsViewAngles;    // Command view angles (world space)
         int                m_nButtons;            // Attack buttons.
         int                m_nOldButtons;        // From host_client->oldbuttons;
         float            m_flForwardMove;
         float            m_flSideMove;
         float            m_flUpMove;
         
         float            m_flMaxSpeed;
         float            m_flClientMaxSpeed;
     
         // Variables from the player edict (sv_player) or entvars on the client.
         // These are copied in here before calling and copied out after calling.
         Vector            m_vecVelocity;        // edict::velocity        // Current movement direction.
         QAngle            m_vecAngles;        // edict::angles
         QAngle            m_vecOldAngles;
         Vector            m_vecAbsOrigin;        // edict::origin
         
     // Output only
         float            m_outStepHeight;    // how much you climbed this move
         Vector            m_outWishVel;        // This is where you tried 
         Vector            m_outJumpVel;        // This is your jump velocity
     
         // Movement constraints    (radius 0 means no constraint)
         Vector            m_vecConstraintCenter;
         float            m_flConstraintRadius;
         float            m_flConstraintWidth;
         float            m_flConstraintSpeedFactor;
     };
     
     
     //-----------------------------------------------------------------------------
     // Purpose: The basic player movement interface
     //-----------------------------------------------------------------------------
     
     class IGameMovement
     {
     public:
         virtual            ~IGameMovement( void ) {}
         
         // Process the current movement command
         virtual void    ProcessMovement( CBasePlayer *pPlayer, CMoveData *pMove ) = 0;        
     
         // Allows other parts of the engine to find out the normal and ducked player bbox sizes
         virtual Vector const&    GetPlayerMins( bool ducked ) const = 0;
         virtual Vector const&    GetPlayerMaxs( bool ducked ) const = 0;
         virtual Vector const&   GetPlayerViewOffset( bool ducked ) const = 0;
     };
     
     
     #endif // IGAMEMOVEMENT_H

The only problem is that there is a CBasePlayer parameter and that isn't (easily) accessible through a plugin .