As Steve said, you can add the redirects as name=value pairs to a data group and scale it up to ~100,000 entries in current versions. The performance shouldn't be impacted significantly by higher numbers of entries as it's a hashed list.
https://devcentral.f5.com/Tutorials/TechTips/tabid/63/articleType/ArticleView/articleId/1086424/Comparing-iRule-Control-Statements.aspx
You can use the class command to look up the requested URI and map it to the new URI.
https://devcentral.f5.com/wiki/iRules.class.ashx
Aaron