If the MLO is a load side panel in the same building, there is no issue with the disconnect. This is only a 225 issue.
If you think the AHJ will buy the idea that there are only 6 breakers in a 20 slot panel and that is all there will ever be, go for it. Worst case is you are going to have to install a back fed main breaker with a clip. Say that is your plan if they ever decide to upgrade.
