The characteristics of failure from oil coking (from not letting a turbo cool a bit before stopping the oil flow) and from compressor surge are very different.... if you have a mind to do an autopsy.
If he wanted to know what killed it your friend could have found out.
I'm glad everyone knows what it is and why it sounds that way... The only way you're going to get that sound without the oscillating manifold pressure and erratic valve behavior would be to add more piping with a mechanism to create the effect (I'm thinking copper pipe and ball bearings, reliefs cut in the pipe above the ball bearing's resting point).
Keep in mind that at low pressures (where it's more likely to occur) isn't always going to cause a problem, it depends a lot on the rest of the system and the health and design of the turbo. The reason you hear a lot of highly tuned cars make that sound it that the BOV is intentionally tuned that way. This allows for a slight increase in responsiveness while shifting but once the system starts bossting past what they consider to be a critical level it will open properly and the flutter sound will stop. Some people do it just for cool points though. A lot of high end race cars employ multiple BOV's each set at a different flow and trigger pressure. A small BOV used at lower boost levels to bleed just enough to reduce surge but leave enough pressure for a quicker return to positive pressure after the shift, then another large unit to dump at higher pressures. I know, an even quieter solution isn't what you're looking for... sorry.