Don't touch mah pike god damnit!!!
As to the GL, I don't think this is possible. afaik it can either attack both while mounted AND while on foot, or neither. I don't think it's possible to do either/or.
Also why should the pike be nerfed because of the GL? That's like saying I want athletics to give me the ability to run as fast as a horse because otherwise cav are OP. It's a weapon to be used on a mount, not a footman's weapon. It's 2 slot for a reason. Pike is 3 slot and CANNOT BE USED WHILE MOUNTED.
The GL needs to be changed, it's a broken weapon. But nerfing a completely unrelated weapon is not the way to fix it.