Here is a quick and dirty video of one of bond1's excellent brutes becoming a sitting duck
http://dcforums.org.uk/fpsc/Sitting_Brute.wmv
Sorry I only have Fraps and do not know how to make it capture the entire screen, so you cannot see what I am clicking in the menus
1) open model
2) select the bone you wish to bend (rotate) the mesh on. I chose the belly button bone ^_^
3) set rotate on primary bone and lock all axis except X (the left right one)
4) use select vertex and select all the ones below the bone your going to bend on, or the part you wish to bend (rotate)
5) bend the sucker to how you want.
6) you can now delete the skeleton if you want, I did and left one bone at 0,0,0 location. Then used the Transform menu to sit the model on the floor.
7) delete the animation, as that's of no use now.
8) your done, export your model as a new name (also do not flip handedness as it is already an imported .x file and not needed)
9) copy over to your FPSC entity folder (place in same folder it came from) and make a clone (copy) of the .fpe the original model used and just name it "sitting brute" or whatever and make sure you update the brute.x part in the .fpe with your new mesh name.
Your done

Here he is sitting in game.

and the moral of the story is Smoking Kills :p