You can accomplish this with a rewrite rule.
You want to be able to use http://proxy.company.com/pacfile as the location for the PAC file you can make a rewrite by using and modifying the CPL below.
Where 18.104.22.168 is the ip address of your proxy, and http://proxy.company.com/pacfile is the url you want to point to.
define action rewrite_pac
; Note: If you are using a non-standard HTTP service on the proxy, use that in the above policy instead of 8080.