I also would like this feature. As it happens I have also tried out the free Cisco Meraki Systems Manager which is an alternative MDM solution and it does have a specific function to allow you to upload a mobileconfig profile which it can then push out to client devices. I created the mobileconfig file in Apple's iPhone Configuration Utility and I then hand edited it before uploading it.
The nearest option I can see in ProfileManager is the 'Custom Settings' option down at the very bottom of the list of settings that can be configured. Even though it does have an upload option it did not accept my standard mobileconfig file. However it might be possible to define the the same settings as key value pairs.
You might want to send Apple feedback requesting this as a feature via http://www.apple.com/feedback/server.html or if you have access https://bugreport.apple.com
It should be noted you can email mobileconfig files to users/devices or make them available as URLs on a webserver, these are alternative methods of distributing them.