Hi Lu Wen, you can use the Navigation widget for this.
So the Navigation widget itself can bring up mashup in either the same window (replacing), a new tab (new) or as a pop-up both as regular or modal.
It also has a Service called Navigate which you can invoke with the Grid double-click event.
The Mashup you specify for the Navigate widget, should have Mashup parameters that can be used to pass information in from the Selected row of the data source to the grid into the pop-up mashup.
Note: You can also pass information back from the pop-up if needed and fire off a refresh on the close of pop-up also available on the Navigation widget.
The navigation widget has an option called Transparent so it can be on the mashup but not be visible.
FInally, you may need to use the Configure Bindings window from either the Navigation Widget or Grid perspective because you wont be able to drag and drop the double clicked to the navigate.