[Templates] Filters + replace

[andrew3@black1.org.uk]

I am trying to expand some text from a number of files.
Each file has an announcement in it. The first line is aubject 
and the rest text.

I would like a filter that
  - takes the first line and makes it <h2>....</h2>
  - processes the rest in the manner of html_para

A number of ways of hacking thos
 - Is there are filter that does something along these lines
 - is it possible to create my own filter - cant see description of how
   to do it
 - I have tried to do [ INCLUDE filename | replace( 'soemregex',
   '<h2>$1</h2> )
   but the $1 bit doesnt seem to work

Cheers