That should already be possible...
(Oops - I removed the explaination of it from the Stereo Tool window and I haven't described it in the help pages either... Bad me! (AU! hitting myself...)
In Stereo Tool, you can include a text file from the hard disk in the RDS signal.
All you need is a way to refresh the text file when a new song starts. In Winamp, there are several generic plug-ins that can do this. For other programs, check if the program has an option to write this data to a file...
Say the data is written to C:\currentsong.txt . Then place \R"C:\currentsong.txt" in your RDS string to add the text to the RDS signal (\R includes a file and converts the text to capitals. \r does the same without converting to capitals. \F and \f do the same, but the included text is interpreted as an RDS formatting string, so it may contain / < > etc. to control scrolling, display speed etc.)
Example: <NOW PLAYING \F"C:\currentsong.txt" ON HALFDEAD-FM
NOTE: When trying this out I noticed that some thing don't work exactly as they should. I'll look into that. For now, just use scrolling (<) to show the entire title.