And I’ve been thinking along these lines - though this doesn’t work:
FWidgetPath WidgetPath;
TSharedPtr<SWindow> ContainingWindow = FSlateApplication::Get().FindWidgetWindow(m_EditText.ToSharedRef(), WidgetPath);
if (ContainingWindow.IsValid())
{
UIArea scaled = GetArea();
FGeometry ChildWindowGeometry = ContainingWindow->GetWindowGeometryInScreen();
FSlateLayoutTransform transform(scaled.GetTL());
auto geom = ChildWindowGeometry.MakeChild(scaled.GetExtents(), transform);
m_EditText->Tick(geom, 0.f, dt);
}