PURL does exactly this. See http://drupal.org/node/292932#comment-1669856 for example.

--
Kyle Mathews

Blog: kyle.mathews2000.com/blog
Twitter: http://twitter.com/kylemathews
Company: http://eduglu.com


On Mon, Oct 4, 2010 at 10:11 PM, David Cohen <drupal@dave-cohen.com> wrote:
I have a module which implements custom_url_rewrite_outbound() (in D7,
will implement hook_url_outbound_alter()).

A user of my module has requested a change; that I honor a special
option which changes the behavior of my url alter.  For details see
http://drupal.org/node/931660.

So to be clear, this would be a new option passed in the $option array
to Drupal's url() and l() functions.  An option not documented on
api.drupal.org, but passed through and honored by my module.

I actually like the proposed patch, and want to include it in the
module.  I just wanted to ask here first: does anyone see a problem with
me using the url $options this way?  Do any other modules do this?

Thanks,

-Dave