Yes, sure.
Why not an AK-47 or a main battle tank? Pink Flying Elephantzs anyone? Wait, it´s already there! It´s called couching from a Noldor Spirit Horse using a LANCE! Have something overpowered made even more overpowered!
A Rune Lance is totally useless. And for the dedicated slicer polearm user, there´s the Glaive. Which you can´t couch but has a nice enough length to safely poke things dead.