To close it with out welding around the internal flapper, you can take off the internal waste gate actuator, then use a piece of flat bar, drill a hole, put it over where the actuator rod normally connects to the internal flap, pull the flap shut then tack the bar to the outside of the exhaust housing to hold it shut.
(when you remove it you just grind it off the outside of the exhaust housing and you wont hack it up like if you tried to remove weld around the internal flap.
The down side being the internal flap may leak a bit slowing spool compared to welding it completely shut, but i cant see this being any different to how the internal gates are sealed by the spring pressure and will start to blow open before it reaches the set pressure and fully opens.
Some people even use this method but wire it shut rather then using some flat bar tacked to the outside of the exhaust housing.
Or if you want to weld the internal flap just use one or two small tacks rather than a full weld around the flap and then die grind them off it you change you mind or want to sell, bit more messy though, and if you want to sell it later you don't want it to be hacked up.
