Sitemap Generator writable file problem

Greetings:

I’m getting ready to activate the Google XML Sitemap Generator. There are 2 files which need to be given write permissions – sitemap.xml and sitemap.xml.gz. The way my hosting is set up, I cannot give write permissions to individual files – it has to be whole directories. I would prefer not to do that for security reasons. Does anyone know how I can edit the sitemap.php file (I assume this is the file I need to deal with) so it points to these 2 files in a directory other than the default?

Thanks.