sorry to be a pain but can you explain your method of cracking open the torso ?
I used a razor blade (brand new and sharp is key here) to cut through the seam along the shoulders. Took a thin hobby screwdriver to pry it open a little bit. Then continued to cut the seams going down the ribcage areas on both sides. Keep prying until you can get the arms out. I just went ape and split it totally apart. You can glue it back together.
You will also need to trim the pegs on the clone trooper shoulder joint so they fit in the shell. I cut them off right where the straight part and tapered section meet. Go into the tapered section and the arms will be loose. (I failed at this the first attempt so I'm trying to save you some heartache here).