If anyone is still interested, supposedly SDK's Mod has finally been ported to Bukkit, including SDK's guns, grappling hook, and utilities. I haven't tried it myself yet so cannot vouch for how well it works, but it's another available option if anyone wants a grappling hook and is fine with client modification.
i think this isnt inpossible. if someone could connect flying and fishing rods, u could use the fishing rod as grabbing hook.
xLevel used to have a skill that was a grapling hook (similar). So if someone could update it then there it is.