The point of a re-routed dumptube is to not disturb the exhaust flow out of the turbine. Most guys just run it down below under the oil pan area and merge it before the cat. Also, I would try to weld it so that the dumptube enters the main downpipe at an angle instead of 90 degrees into it (like pictured).
And yes, an internal WG can still utilize a dumptube. Like a DSM setup, the O2 housing (first section off the turbine) can be seperated into two sections, like this:
