If you want to retrieve user's manager information, it must exist somewhere, right?
SharePoint cannot fetch data directly from Active Directory (obviously because not only Windows authorization is supported), it uses User Profile Service as an "adapter". If UPS is not configured, SharePoint simply doesn't know from where to retrieve the information needed to provide the manager functionality.
Thus, if you have your own custom source for such kind of information (it could be SharePoint List, Excel file, AD, etc.), and you don't want to involve User Profile Service, your best option would be to create a custom workflow activity and retrieve the needed information through the code. Assuming you're using SharePoint designer, have a look at the following article:
Also you could prefer to build sandbox-enabled activity so it could be used in Office365 (please keep in mind, that all the SharePoint Sandbox limitations are applied to this kind of activities). In this case, the following Wictor's post would give you a great start: