EFI Solutions also has the rubber stopper bit. I did this on my R34 and had to take apart the lower section of the steering column for better access of squeezing the bloody thing in there.
Same symptoms I had when mine was failing on a r34. As I took it to my mechanic to get it fixed I'm not sure on where to buy them from. Hope you find asap as its feels bad to be part of those douches that don't indicate.
Are you forgetting that the stock boost of the R34 is 7 PSI. This is just bypassing the 2 stage boost solenoid to run the full 7 PSI from 3000 RPM. He will have the same boost even after doing this mod......unless he drills out the restrictor hole.