Currently, you press (starting from the WPS) "long select, right, right, long select, right" to remove the currently playing song from the current dynamic playlist.
Thanks Chronon for your tips, many of you are of course right and I can understand why you do not want to support such custom modifications officially.
Maybe in future more and more people can start forgetting old "standard behaviours of players" no matter which modes we defined where. I looked at the problem as how often I use certain operation sequences, and put them together into a single button press. As Rockbox is open source anybody is free to implement whatever they want for personal use. I will do when the time comes, until then I will continue using my mobile phone.
What would be the fastest key sequence for adding current song into an existing playlist like e.g. "favourites"? Also this I would prefer sitting on a single key press.
For me increasing the quality of my music selection in the long term is far more important than fast forward and rewind. I do not have a need for fast forward and rewind as I use a separate, special mode which does it automatically. But again, switching into and out of this special playback mode should be possible in a direct and fast way.