Vista - BitLocker: How to change drive letter S:

I installed BitLocker using MS "BitLocker Preparation Tool". Now S: is my
system partition and I cannot change this drive letter. Since we use software
that wants some data being located on S: I need to change this letter. I
found no 'regular' way to do this.

Would it help if I disable BitLocker, use letter S: for example CD-ROM or
something and then (when S: would not be available any more) re-install
BitLocker? Then I could change CD-ROM letter back to whatever and use S: for
this software.

Best regards,
Robinio