There is no need for migration cockpit in this case. I have done this a number of times so far. Just follow the simple steps in your DEV client to prove the logic.
Asign the old Company code to the non lead ledger. Even if it has 2 years of data.
Now use the program: FAGL_DELETE_RELOAD_LEDGERS. This program will copy all the previous years transactions to the non lead ledger of the company code you just assigned. The program first tries to delete the data in the non lead ledger data specific to this company code but there would be nothing to delete because you just assigned it to the parallel ledger. After that it updates all the records to the non lead ledger of this company code. run this foe each year individually. If you have to catch up 2 years data. Start first with 2014 & then 2013. Run Trial balance after that. It will match to the penny. I am 100% sure.