The high lighted part is little more involved than that. A TDI without a load on it will not come up on boost if you increase the RPM's.
Although I respect what you say, and respect your exprience I have to argue that boost comes up enough to diagnose some or most leaks. If it doesn't ID the problem just the original poster can try your "3 footed" (hope he don't get run over by his helper) method. Of course original poster may have an auto, then it would be 2 footed.
I can remember many that I identified that way, including...
1 BHW with split in lower intercooler hose just last week
2. Found two BHW "elbow" hose split this way.
3. Several ALH cars that had never got the clamp reinstalled on the lower intercooler pipe, after we worked on them. (self inflicted) These would "sing" on the road under hard boost. Kinda weird.
4. Several more ALH carsthat the lower pipe popped off, for whatever reason.
The main point of my post above is that the other comments went to sticky vanes on the turbo without eliminating the obvious. the beauty of these forums is you get several view points and of all of them hopefully one will point to the solution. I've been trying to make some youtube videos, to share some of the knowledge I've gained from running a VW specialty shop for 7 years now. Unfortunately its tougher to make and produce good content than I thought.