The guy is correct really, they are not the correct solution in an ideal world but people want a low cost easy to do method of changing boost, so they are used.

The controlling of the boost I'm not sure about because I dont know how the ERST ECU works, but it should be possible as it has an amal valve doesn't it? Provided that you can modify the point at which the amal valve kicks in then yeah its totally possible.

JAmes.