How can I override or add NotesXspDocument to XPages events?

I have a custom control to which I pass the data source. Property of the customecontrol.xsp-config property:

<property>
  <description>The src Datasource source data (WIP)</description>
  <display-name>Source Datasource</display-name>
  <property-name>srcDatasource</property-name>
  <property-class>com.ibm.xsp.model.domino.DominoDocumentData</property-class>
  <property-extension>
    <required>true</required>
    <designer-extension>
      <category>1. Workflow Parameters</category>
      <editor>com.ibm.workplace.designer.property.editors.dataSourcePicker</editor>
    </designer-extension>
  </property-extension>
</property>

I want to add some logic to querySaveDocumentthis data source with code in a user control beforePageLoad. This logic will add reader and author document elements to the document, as well as some other control values.

How can I add my code to this event?

Thanks in advance...

/ Newbs