I've really only just discovered that you can use /** @blah */ comments to specify certain things, but is it possible to create sections in code?
Like:
/** Start Section "Blah" **/
$result = doSomething();
echo $result;
/** End Section "Blah" */
No PDT can't do that. Generally expandable code sections are identified by function and class method bodies.
If you think you need artificial sections identified by comments I recommend to rather think about reorganizing your code into more fine grained files, function, classes and methods that can be easily documented using PhpDoc (which is the standard PDT uses).