Python Add-In Dialog with Textboxes in ArcPy?

With Python Add-In Wizard I created a ButtonTool with which I:

1. click in the map
2. get the coordinates of the mouseclick-location in a dialog with textboxes

I want to receive the coordinates in a textbox to have the possibility to copy and paste the coordinate values (e.g. to use them in a document).
I get a crash between TKinter and arcpy like I read in some posts before. Nevertheless I want to ask, if anybody has experience with this and has a suggestion.

Here is my code:

Import Tkinter
class ToolCoord(object):
    def __init__(self):
        self.enabled = True
        self.shape = "NONE" 
        self.cursor = 3
    def onMouseDownMap(self, x, y, button, shift):
           pt = arcpy.PointGeometry(arcpy.Point(x,y))
           main = Tkinter.Tk()
           lb = Tkinter.Label(main, text = "UTM-Koordinaten:")
           lb.pack()
           t1 = Tkinter.Text(main, width=20, height=0)
           t1.insert("end", str(x))
           t1.pack()
           t2 = Tkinter.Text(main, width=20, height=0)
           t2.insert("end", str(y))
           t2.pack()
           main.mainloop()