OK here is one very hand to hand (long) manual solution, from one jonescincy, DMT has not tried it yet. If you are super keen, let us know how it goes. I can't believe there isn't an easier (quicker) way!
There is a simple solution to get access to the files after running migration assistant.
First you need to navigate to the User the files are created under. Go into Finder and search This Mac for users. You should find a Users folder that has your Mac user name and at least one other name that contains the migrated files.
If you double-click on the migrated account you may see a red circle with a - sign.
If that exists, all you need to do is give full access rights to yourself (main user account/admin).
To do this "right click" and go to Get Info. A box will appear and show the properties.
At the bottom, click on the lock and enter the user’s password (assumed you logged into the main user account which should be the admin account).
You have now unlocked the properties and can set them to whatever you want.
Click on the + sign at the bottom and add the main user by highlighting and hitting select. This will add the main user to the list in Read only.
Click on it to change to Read and Write.
Next click on the little gear icon at the bottom and select the option to copy the settings to all enclosed files and folders.
The red circle with the - should now go away. You are now free to move files around in that folder as you wish.
All folders will need to be done separately so my suggestion is to get as close as you can to the root and change the permissions as described above.
If you have unlocked a music folder for example you can now copy its contents into the users Music folder.
Once copied and verified, you can delete the orignal set of files and then eventually the user, by going into system preferences under utilities and selecting Users and Groups.