Hi Dan,
On your dialog, are you passing your parent datasource to your dialog via a property definition (com.ibm.xsp.model.DataSource)?
<xc:ccMyDialog parentDataSource="#{document1}"></xc:ccMyDialog>
If yes, then you should be able to access it via SSJS in an onclick event to pass your data back to the parent datasource & then close your dialog.
/* Get a handle to the parent datasource */
var parentDoc:NotesXspDocument = compositeData.parentDataSource;
parentDoc.isEditable() ? parentDoc.replaceItemValue(<your code here>) : null;
var d = getComponent('partyDialogBox');
d.hide('closingBookPanel');
Is there any way you can rewrite your dialog so the cell uses a standard link control; then you would have access to both the CSJS & the SSJS?
Sometimes I've had to stuff values into viewScope variables, and have hidden controls bound to those viewScope variables -- then you can get a handle to the values via CSJS using XSP.getElementById("#{id:<yourHiddenControl>}"); and also via SSJS.
Maybe none of this is helpful, and you can't do anything like that in your particular situation.