Insert data into open file binarywriter/filestream

Question

I'm currently reading a file in through the binaryreader class and I can successfully write it back out using the binarywriter class.

What I am trying to find out is how to insert data into the file. Whether reading it all in, inserting what I need to and recreating it byte for byte I don't mind.

binarywriter doesn't do what I need to do as it doesn't insert, only writes over.

What options do I have on inserting data (shorts/bytes ect) into a file.