i feel your pain man,
when you run with bayonet attachment you do see the model in a charging posistion.
but im clueless aswell.

Okay i figured it out lad!

so what you do is open the developer console and type in: cw_kk_melee
copy paste it if you want. after that type the key you want it bound to.( in my case mouse 5)
so the command woul look like this: cw_kk_melee mouse5

bind (key) cw_kk_melee put this in consule but put a key for the bayonet