Set email signatures for all users in Exchange Online?

Is there currently a way to set email signatures for all mailboxes in Exchange Online, without the use of a  paid product, and without the use of email flow rules to add disclaimers? 

It looks like there used to be a PowerShell module that did it through use of the command Set-MailboxMessageConfiguration. As far as I can tell, that hasn't worked since the switch to roaming signatures.

I've looked at the PS module ExchangeOnlineManagement but that only seems to have a handful of commands, and nothing useful, as far as I can tell. The documentation on that module is a disaster.

Thanks in advance!