The simple solution is to unpack the model, remove the bone on which the strider's "weapon" mesh
is attached (I don't remember its exact name, I think it was "bip01 head"), similarly the landing bone will need to be rotated along the axes so they coincide with the position of the player sitting on top. After that, reassemble everything back into the pack.
P.S.: If you don't understand what I'm talking about here, go to someone like •°•°•PsycHoO•°•°• and buy a ready-made solution from him, don't waste your time.