how to make ‘siteurl’ malleable?

or, really, would just leave it blank, except I know that’d break everything, and it looks like I’d have to go in, clean the cache, then go into the db and re-enter ‘siteurl.’ what I’m playing with, though, is feeding two domain names into one wordpress install. so I’m rewriting the URLs. it’s working great (demontheory.net/stephengrahamjones.net), except, for the wp_list_pages() and _categories, I think they’re called. when the URL’s set to ‘stephengrahamjones.net,’ those links are still output as ‘demontheory.net’ (ie, the siteurl). which is why it’d just be so much easier to have that site url blank somehow. anyway, I’d guess people have run into this many times before, and there’s some easy and obvious fix. thanks for any help, anybody.