The only domain requiring a glue record is the box hostname. The rest of the domains can make use of MiaB as with any other mail server, which I assume you are already doing since Cloudflare does not offer email hosting service.
MiaB has an API for DNS and it is documented on the ‘Custom DNS’ page of the dashboard. I don’t know anything about Lexicon, but it would be up to that project to make use of the MIaB API.