Target A GridViewRow With An AJAX.Net Toolkit PopupExtender?

I have a lot of data to display in a GridView. Because there's so much information per row, I'd like to be able to display additional information when a user clicks on the row, so I thought a PopupExtender from the AJAX Toolkit would be perfect.

Ideally, I want the popup to display whenever any of the controls within the row are selected. I've been able to successfully attach the PopupExtender to a single control within the row, but I can't get the pop-up to attach to the row itself.

I would have thought that setting the PopupExtender's TargetControlId to the Row's ClientID within the RowDataBound event would work, but when I do this I get a runtime error:

TargetControlID of 'popupExtId' is not valid. A control with ID 'gvList_ctl02' could not be found.

I noticed that the GridViewRow is rendered, the tr element does not include an id, so I also tried extending the GridView control to override the CreateRow method to render the id - using this method I was able to render the row's ID (e.g. gvList_ctl02), but the same runtime error was thrown when I added the PopupExtender back into the code.

I also tried binding the showPopup() javascript command to the row's onclick event to get the popup to display manually; whilst the click event is registered OK and is definitely triggered, the popup is still not shown.

Does anyone have any idea how to / if you can bind a PopupExtender to a GridViewRow?

My row bound code is as follows:

protected void gvList_RowDataBound(object sender, GridViewRowEventArgs e)
{
if (e.Row.RowType == DataControlRowType.DataRow)
{
// Bind the popup extender's target ID to the row ID
// This will cause a runtime error
PopupControlExtender pop = e.Row.FindControl("popupExtId") as PopupControlExtender;
pop.TargetControlID = e.Row.ClientID;
// Also bind the client side click handler to try to get the popup to show
// The alert is triggered and no javascript error is generated, but the popup does not display
e.Row.Attributes.Add("onclick", "alert('Row Clicked'); $find('" + pop.BehaviorID + "').showPopup();");
}
}