Thank you for writing.
Please refer to the following documentation article: http://docs.telerik.com/devtools/winforms/pivotgrid/pivot-field-list/customizing-radpivotfieldlist
I can suggest using the second approach handling the AddingContainerNode
event and to cancel it for any fields you would like not to see in the pivot field list.
I hope this helps. Should you have further questions please do not hesitate to write back.