Are there any 'hooks' in the pager, or can one replace it?

I want to write a simple filter to run text through before displaying
it in the pager.

Can one either 'hook' incoming text somehow or replace the pager
completely with an external program?

I simple want to change incoming quoted text on a couple of groups
where quoted text is marked as follows:-


[quote] This is the quoted text, possibly
on multiple lines.
[/quote]

to:-
> This is the quoted text, possibly
> on multiple lines.


-- 
Chris Green