Since its Mass Air Flow and not really "load" that causes boost to be built, if a car has a small turbo and a rev limiter, you could mat the gas pedal and bounce off the rev limiter and theoretically build boost.
i was able to build boost in my 87 GN with it in park by revving up the engine to 4000 then let off the gas.
then proceeded to do this 4 times in a row and the car built 10 psi of boost-
it seemed kinda odd, so i never did it again, just didnt feel right to have boost and not in gear
boost gauges are plumbed in after the TB not before. and since boost is measured in positive manifold pressure technically it IS boost. for your sake tho we can call it "poser boost" since it is just acting like boost and isnt REAL boost.