Making line prefixes invisible to a mode?

[Raffaele Ricciardi <rfflrccrd@gmail.com>]

Hello everyone,

Emacs supports multiple major modes by means of indirect buffers. This
feature is useful - among other things - to edit comments in source
code.  However, when editing a block of line-comments, the
line-comment prefix is seen by the alternative major mode as a part of
the buffer (unless such mode is a specialized mode, of course).
Narrowing can't work, either, because you can't narrow to a rectangle,
can you?  Therefore, is it possible to make a mode "believe" that each
line starts after the line comment prefix?

I have an alternative solution in mind*, but I'd like to know whether
a direct way to achieve this is available.

Thank you.

*: Such solution would involve narrowing to a comment block and then
  stripping the line prefix, only to add it again before widening.