I think he still has to understand the absolute paths to the respective directories on both sites in order to craft a relative address on the gosport site in wxstatus.php to the GR3 directory in the mikeswxblog site (assuming that BOTH are under his main hosting directory).
the realpath() function won't help unless you know the exactly what relative file addressing needs to be used -- it would then flesh out the absolute path for you, but you have to start with a good relative file path in the first place.