return file from memory

[Charma]

Once again i have a problem abusing this forum for help, sorry.

I am looking for a way to return a part of a File in a function without writing it to hdd but sending the part itself as a File.
Maybe someone has an idea how to do that?

File myfunction(...requestedPart...)
{
  File bigfile = new File(bigfilename, FileMode.In);
  ...
  bigfile.read(request, requested part);
  ...
  return request;
}

Now i want this "request" not to be a string with the content but a File-Type itself without saving it to hdd. I want it to be saved in memory only but be able to handle same like File-type. Anything like that possible?
Maybe i need to make my own class from File or something?!?
Thanks for any help!