Rue, the exercise machines will be helpful, but may not be perfect. Try the one for the legs. Also the cheat, slow_motion 5 (or any number between 1-8 ) will slow down the animations so you can get the exact pose you want. Remember to use, slow_motion 0 to get the speed back to normal.
Also, there are the "slot enable packages" at MTS2
here and another one
here they are what are used to place sims on objects such as a decorative horse. There also is the magistray
here which you can place extra things on tables or other objects. I put my sim on the tray, then the tray on the slot enable package thingy and then move it to the object I want them to pose on. There are invisible recolors included. Check the threads for what EPs may be needed for these.
Please remember[/u]: never save the game with your sims on these, you will not be able to enter the lot or in my case, get them off of the tray. Read this
here before you use this it explains the warnings.