Yes, this is possible.
I'm assuming you have access to make changes to the form and that you're not talking about a form on some other server that you just post to. Based on that assumption, basically, you can put at <TEXTAREA> </TEXTAREA> set on the form, so the poster can put a large amount of sequences.. when posted, have the script parse the incoming info by newlines. Process as needed and save to file.
If you post your code-in-progress, it will be easier to help with specifics.
-Syn0