Thanks for the reply, Bob. A colleague pointed out to me that the .msf that maxlike calls can simply call "sim" on the SystemBuild model in question, and thereby function just as if the model were implemented in the .msf. I can't see a thing wrong with that idea, but I have yet to return to the problem and try out that solution.
(I'm afraid that whoever wrote NI's documentation on maxlike thought that pointing out that "sim"ing a SystemBuild model via the .msf call would be such an obvious approach that it wasn't worth mentioning <sheepish grin>.)