Google Postmaster tools - how to implement with Marketo

Hi everyone

Having some trouble implementing Google Postmaster tools with our IPs. See here: https://postmaster.google.com/managedomains?pli=1

Our IT team has told me that they can't add a TXT record to our DNS configuration since Marketo is on our CName, and "no other records can live with cnames, txt records included." We tried putting it on the "apex", but that didn't work either.

Are we approaching this incorrectly?

Thanks!