Take a look at this thread. A poster said they were able to connect a computer to the MM using two USB to five pin midi adapters and connecting the two adapters via five pin female to female adapters. Your iPad operates as a MIDI host and the MM needs to see it as a MIDI device. Presumably the two devices chained together as described allows that to occur. I’m not aware of a more straightforward method.
On the reported roadmap for the future is an I/O expander that has TRS MIDI in out jacks, but there’s been no information provided on if/when that expander will be released.