I would be very helpful if you could explain why you want to do this, ie, the application?

If you want to split some big file because it doesn't fit on a CD, just open the input file and start writing to an output file. Keep track of the number of bytes written, when its too big, start a new file (outfile_part1, outfile_part2, etc).

I think there is a *nix utility that does file splitting, but not necessarily on line boundaries.

I have no idea at all what you mean or intend by "virtual file".