How to set parameter in order to use it publication sitemap ?

Hi All

I want to set a parameter for a publication which should be accessible 
in publication sitemap. But I want this parameter to be configured from 
the CMS area as well.  To achieve this I have written a usecase. I can 
create a new xml file for this purpose from where i can read and write 
the changes but that will not be accessible in publication sitemap.

I want to get that parameter in the matcher so that I can change the 
flow accordingly.

For example:

I would like to achieve something like language parameter, which is 
accessible anywhere in the publication by using {page-envelope: ...}

Please suggest

Thanks

Gaurav