As far as we understand, there is literally no place to put the ultrasonic information - the data from the original higher sample rate - on an MQA-CD because the data on the CD is 16-bit, not 24-bit. It would seem that an MQA CD either stuffs a very small amount of lossy encoded ultrasonics in the 14th, 15th, and 16th bits, or else it simply uses those bits to encode "authentication" information and the instruction/trigger to the MQA-compatible playback equipment to employ the MQA "apodizing" digital reconstruction filter upon playback.
In this respect, MQA CDs would seem to be even more fraudulent that MQA high-res digital/streaming files, as the MQA CD packaging routinely contains printed statements about "352.8kHz" resolution/sample rates, which (if you'll excuse the contradiction of trying to talk about degrees of an absolute thing like impossibility) is even more impossible than the resolution/sample-rate claims made for digital MQA files.