Actually there is an offhand hook in the mod, you have to set the dmflags to suit your wants
1 No health
2 No powerups
4 No armor
8 No falling damage
16 Fully Loaded
32 Infinite Ammo
64 PowerUps Drop
128 Spawn Farthest
256 Force Respawn
512 Fixed FOV
1024 Enable old Q3 BFG
2048 Enable CTF techs
4096 Allow Grapple to sky
8192 Allow Grapple
16384 Offhand Grapple
32768 No Footsteps Sound
and you need to put this in the console
hookon, hookoff - These commands are used with the offhand grapple, enabled through DMFLAGS. "hookon" fires the hook; "hookoff" releases it. These commands are usually coupled with the +/- command system to produce one "+hook" command (see below.)
+/- command system - Players may now bind together aliases that execute one command when a button is pressed, and another when the button is released, similar to the +/- aliases of Quake2. For example, players often bind the "hookon" and "hookoff" commands into one command with the following alias:
seta hookDOWN "hookon"
seta hookUP "hookoff"
bind mouse3 "+hook"
and then you should be swinging around your favorite map in no time