Grimmspeed makes a bunch of these "Internal Wastegate Bracket"s that hold the door shut if you switch to an EWG. They are cheap from them, but in all honesty, you could make something pretty close to that for very cheap. You might NEED to make one custom for your Greddy turbo. Also, since that's just oil cooled, are you going to run a turbo timer with it?
The internal wastegate(IWG) bracket is used in place of the stock wastegate actuator when moving to an external wastegate setup. In the previous years Subary owners had to weld the IWG shut on their turbos which diminished resale value, had the chance of cracking, and made it very difficult to revert back to the stock IWG setup.
We are bringing you the solution to this problem, the GrimmSpeed IWG bracket. This is a basic bolt-on which takes 5 minutes to install. No more worrying about the wastegate door opening due to a cracked weld, no more worrying about trying to sell your turbo with welding all over the wastegate door. Feel like reverting back to stock?...simple, just unbolt the bracket and you are good to go.
Here's the link to their page. http://www.grimmspeed.com/catalog/index.php?cPath=22