Does there exist a ready-made design for implementing the measurement hardware? You can buy the analyzer package from e.g. Omicron Lab but it's a hideously expensive piece of kit (4490€) considering what you're actually buying. Never mind Ridley's version at $17.5k.
It's possible to measure a SMPS circuit feedback loop bode plot by injecting a signal into the loop and measuring the response. Theoretically you can do this with a signal generator, transformer and 2-channel oscilloscope. In practice it's not that simple - to start with, finding the right transformer to do your testing between, say, 10Hz and 1MHz. Has anyone managed to do that in a reasonable way using "homebrewed" equipment?
Basically what that very very expensive equipment does for you is to generate and record the various test points which is a tedious business at best.