I'm filing as a dual status return as I was a non resident alien for half the year and a resident alien at the end of the year.

My Employer has supplied me with a W-2 that encompasses my entire years income with no distinction between NRA and Resident Alien

How would I file my 1040NR and 1040? Would I manually split the statement? To which form would I then attach the W-2?

Or would I enter all the info in both forms?

Yes, do simple arithmetic calculation.