Take a look at the command line tool rhythmbox-client. Looking at the options there's a --seek switch which should do what you want.
rhytmbox-client --seek=+60
There are reports that this should work but doesn't. Might be a bug?
As an alternative method you can fire the commands directly yourself using dbus:
# seek forward 60 sec
dbus-send --print-reply --dest=org.mpris.MediaPlayer2.rhythmbox /org/mpris/MediaPlayer2 org.mpris.MediaPlayer2.Player.Seek int64:60000000
sleep 2
# skip to next track
dbus-send --print-reply --dest=org.mpris.MediaPlayer2.rhythmbox /org/mpris/MediaPlayer2 org.mpris.MediaPlayer2.Player.Next
sleep 2
# toggle play/pause state
dbus-send --print-reply --dest=org.mpris.MediaPlayer2.rhythmbox /org/mpris/MediaPlayer2 org.mpris.MediaPlayer2.Player.PlayPause
sleep 2
A bit too verbose for routine command line use, so just pop them into conveniently named scripts, and away you go! The list of commands can be found here.