GuillermoRosado,
I think I now understand what you want to do.
* Do not enable the PIANIST button.

Instead.

* Press SPLIT and press the first key to the left of the keyboard before releasing the split. This will be your new split point (which is actually just that one key!)
* With the HOLD function (OFF), you can now play along the keyboard anyway you see best so long as you do NOT press the first key (which you used to assign the new SPLIT point).
Hope this helps.
Thanks,
AJ