PEP being ProntoEditProfesionnal? If you mean PEP, then you can add System Elements to user pages only with PEP2.
You posted in the NG forum so will answer according to thread location.
If you mean PPENG, then the official answer is covered here. [Link: remotecentral.com]
However, I have created my own custom battery icon, clock, etc and put it on a non-system page. The issue is that you cannot edit any of the properties in PPENG, you must edit them by hand. This is done by hand-editing the ConfigEdit.XML file inside the PCF zip container.
This requires you to have knowledge of the PCF xml schema and be able to 'inject' your own bitmaps into the configuration outside of PEP.