If I understand correctly, you are now wanting to migrate from the MacBook to the headless Mac Mini after the fact?
If so and if you could, it would ultimately give you 2 accounts on the headless Mac MIni. The one you initially setup and a second one from the MacBook.
Personally I only see 1 good option and two that will only allow you to manually move your User Data to the Mac Mini.
- Start over! Use a Keyboard, Mouse and Display, completely erase the Mac Mini and do a proper Migration from your TM backup.
- Manually move your User Data over to the Mac Mini using an external drive, flashdrive or perhaps (depending on the size) over to the Mac Mini via Ethernet.
- Pay for an expensive FireWire adapter and hope that you can use Target Disk Mode to connect the Macbook and Mac Mini together and again, manually move your User Data over from the MacBook over to the Mac Mini.