boost controllers are a very good idea, especially when you can build an adjustible one for about 5 bucks.
Eddy google DIY Dawes device and it will show you how to make one with a few plumbing supplies.Mine cost me £10.
It's been at least a couple years since I've had one of the KKK turbos and so my memory is a bit foggy, but I was under the impression that the threads to the wastegate screw were inside the top of the can. That's why I was asking for a picture. The top of the wastegate can is also mild steel, not copper. If it were mine I would weld a new nut to the can. Other options would include carefully undoing the crimp of the can and pulling of the top and installing (glue or weld) a nut to the inside so that it was pressing on the can top rather than being held by the glue, or you could try to find someone with a knackered version of that turbo to steal the wastegate from. If you go that route, bear in mind that the K14 and k24 wastegates are not interchangeable even tho they look the same externally.
Using a BOV for boost control is a bad idea. It would basically be a big boost leak and hurt engine efficiency and the way it dumps boost really hurts drivability.
just did a 1200+km trip this weekend, no wastegate or bov enabled pump adjusted, burnt a tank n a half of fuel, but never seen over 13psi no matter how hard i was on the throttle, i was going along a flat spot at about 160km/hr and about 14psi was the highest it read, i think my wastegate is garbage, and i cant get it out to clean the seat for it or block it off, what the heck do i do...... other then that i only had a minor issue, my alternator was over charging cause my heater blower died and was drawing some crazy amps... so i went to shut off the blower cause it was smokin and smelt nasty and i found out my switch control had melted, good thing where i was happend to have a wrecker full of imports so i got a new control and blower motor all for 45.00 good deal i figuree.