Changing pitch without changing speed is very hard without introducing artifacts, stations that do this indeed speed up the playback. For small speed changes you won't notice the speed change, but you will notice the pitch change. It makes very little sense to put something like this in Stereo Tool, it's indeed really something that they playout software should do.
It would atleast be helpful I think if Stereo tool could include this. I've tried many playout softwares and none of them offer this ability.