i have an internal gate 10cm^2 td06 exh housing, similar design to that, just get the round section blocking the wastegate removed. You can see a small butt of weld where it can be removed... It seems as tho you would not be able to have a collector style dump pipe on it seeing as there is no stud nor flat face for a gasket to seal on. I'd suggest a split dump, using the existing dump pipe and have a pipe welded to the housing behind the w/gate which you can merge with the main exh further along the system (and block the section which joins the two).
That or leave it as is, but its a restrictive looking setup