With the awesomeness of GPScript you can!
Var
PLAYSTOP : Widget
On WidgetValueChanged(newValue : double) from PLAYSTOP
If newValue == 1.0 Then
EnablePlayhead(true)
Else
EnablePlayhead(false)
End
End
I have attached a sample gig file so you can see it in action.
Widget to Play-Stop.gig (5.5 KB)