In PR 1.1, Media Player would update the labels itself. Unless you wish to replace /usr/bin/mediaplayer.launch with PR 1.1's one...

Anyway, since I don't get how FM RDS Notify works, I made a quick hack for myself.
Run "fm" in a Terminal, and when (and only) the FM transmitter is on, it'll send the details of the currently playing track.

Designated thus:
artist == "rds_ps"
title == "rds_text"

"rds_ps" is limited to 8 characters, I believe and "rds_text" to 64 characters so the required cutting will be performed if necessary. If the file has no artist information, rds_ps will be set to "Nokia" and if there is no title information, rds_text will be set to "(unknown song)".