Hi David,
The attached sample may fill up your requirement,regarding PopupControlContainer over the GridGroupingControl.
Actaully this Sample is the modified version from the link,
http://www.syncfusion.com/support/forums/message.aspx?MessageID=48626
The PopupContainer is made in such a way that it may popup when the user "Right Clicks" over the Button in Header of the Grid.
The handling of all client-side functions, mentioned in the sample, were made from the Server Side by specifying the parent control''s ID.
And too, its not possible to get the column header index from the popup control because we show the popup with respect to the header cell and not with respect to the button. So according to now we need separate poups for each columns.
I hope this Sample may help you and give the solution of your problem.
PopupMenuUnderGrid
Thanks,
G.Pradeep.