issues Proxying to a different URL

I’m working on proxying blog.thedomain.com to https://www.thedomain.com/blog, but having an issue that’s difficult to resolve. For security sake, the blog.thedomain.com subdomain has access blocked outside of our internal network. I’ve set the WordPress URL to blog.thedomain.com and the Blog URL to https://www.thedomain.com/blog in the WordPress general settings, but the bloginfo() still references the blog.domain.com address, so things such as javascript, stylesheets referenced using template_url and many plugins don’t work on the https://www.thedomain.com/blog site that we want to have as the blog location available to the public.

Any idea on how to change the URL references within WordPress without editing core WordPress files and editing each plugin? Thanks!