The problem seem familiar. I think I've seen people to run into this before. I don't have any 8GB file myself to try with.
I know that it is common in the MySQL world with exporting data as INSERT files, but that is not really what we do in the SQL Server world.
I think you will have to cut the file into several files, but I don't know what size you will need to keep SQLCMD from choking. You will have to experiment.