Well, I've written a utility collection script when I was a postdoc in Rob Clubb's lab lab, called "nut".
http://nmrwiki.org/wiki/images/scripts/nut
It has a command built in -txt2rdc
, but I know that scaling parameters and possibly some math inside is broken.
You can find out how to use the command by typing on the command line:
nut -txt2rdc -help
Maybe with nothing better you can take that and improve so that it's actually useful?