Rough stuff. You can't do any kind of redirection without access to DNS, apache config, or the docroot (your HTML, etc.).
My suggestion, shell out for the first three months (the discounted months), and remind your visitors to update their bookmarks. Your new site will be indexed and receive a tad of an initial traffic boost from the links point in from geocities. When the geocities account dies, you can probably expect the replacement site to be in about the same rank as the old one, presuming it's the same content and all referring sites have update their links.