Creating animation rig for a game model with wrong bone orients


I have a model i need to animate, but the problem is, its having all bones oriented wrong, but i need to keep them this way, because other way if i export animation from fixed skeleton to game engine (where i already have this character setup, it will be crooked, cause blender bone orients are different from game bone orients.
Is there a way to create animation rig, without touching original skeleton? Maybe duplicate skeleton, fixing orients and constraint original one to this? Is it possible to do this way or similiar?
Any tutorial or tips?