Load Sonic Stage

. Or click Sonic Stage and go make yourself a cup of tea/coffee. Should be half loaded when you get back.
Tap F1 on the keybroad or go to help.
Once help has loaded click the 'search' tab. Type "Dividing" into the field and seach. You should find some useful results. Read the notes carefully. It seems like it splits up the original audio files. So I would consider making a backup copy of the original track that your about to split.
As it says in the notes you cannot split tracks that are already on the player so your going to have to transfer the tracks again.
Not tried this myself so i cannot guarantee any useful results.