serving a blog at domain.com/blog when dns for domain.com is pointing elsewhere

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http://serverfault.com – there is a blog hosted on one machine (apache) (currently at blog.domain.com) and we'd like to move it to domain.com/blog. dns for domain.com is pointed at an haproxy machine load balancing a few nginx app servers. the machine hosting the blog is not behind that load balancer. considering i have complete control over the configuration of everything, whats the most straightforward way to get this to submit to my will and have the blog served from domain.com/blog? (HowTos)