You can try to use this software, (I did not try this, I just found it on the web)
but as Dave mentioned, you can never trust a program like this!
If it is really important for you, than safest solution is if You make a virtual machine, copy the .pst file in it, than install the program (or any similar programs) on the virtual PC, crack the .pst, copy the cracked .pst back to your PC, and destroy the virtual machine.
This is unofficial but might work.