spiritparse - 1:27 am on Apr 7, 2010 (gmt 0)
On way you could do this using A1 Sitemap Generator or any other sitemapper program that supports splitting sitemaps at custom URL count intervals would be...
Split sitemap generation at e.g. 2000 URLs per file.
You will then just have to edit the generated sitemap index file a little. And then add a reference to one new sitemap-xyz!.xml file every day or week or whatever :)