This is the only way one can do it at this time without reanimating it and to tell you the truth I don't know whether one can do that using FPSC or not since I'm neither a graphics person or an animator.
I use this method but the problem with it is that the positioning of the arms still makes the NPC look weird; since this is a climbing animation. So the only thing you can do is try to add something in front of the NPC to make it appear that he is doing something with his arms or, instead of an idiot just standing there, you will have a dorky idiot just sitting there.