Add LOCALHOST checkbox to form action

Would love to add [ x ] use localhost (same site / same server) instead of full https URL requiring a "round-trip" (ie: leaving the site, going through the network just to end up back at the same server. Instead, using localhost should allow me to: a) select a REST API on the local host that is available (from a drop down), and simply call the function b) possibly execute a do_action instead? or fire off an internal PHP function with parameter mapping? somehow – short circuiting the entire: leave the existing site only to come back process. It would be much much faster this way. Localhost is fairly well understood internally by hardware, and is turned around on the IP card before it ever leaves the machine.