I have a web application that has a custom HttpHandler that has the
following mapping

[url]http://myhost/mywebapp/site/page.aspx[/url] to
[url]http://myhost/mywebapp/page.aspx?id=site[/url]

All pages have a predefined layout based on the site that is handled
by a
common base class.
I use forms authentication that denies all anonymous acces

<authorization>
<deny users="?" />
</authorization>

My problem is that each site has a login page and a register page.
When an anonymous users try to access a page, it gets redirected to
the login page.
I want to make an exception. I want that when an anonymous user tries
to access the register page (registers.aspx), it should be able to do
it.
I know this can be done in the web.config file:

<location path="site1/register.aspx">
<system.web>
<authorization>
<allow users="?" />
</authorization>
</system.web>
</location>

<location path="site2/register.aspx">
<system.web>
<authorization>
<allow users="?" />
</authorization>
</system.web>
</location>

<location path="site3/register.aspx">
<system.web>
<authorization>
<allow users="?" />
</authorization>
</system.web>
</location>

....

but what i really want is not having to add a new entry to the
webconfig when i add a new site (maybe using global.asax
Authenticaticate event) but still using Forms authentication.

Is this possible? if so, how?
Thanks a lot!