Even more pedantically, you'd be measuring the round trip time from the earth to a mirror located near the sun and back, but not at the sun. Does there even exist a mirror anywhere in this universe that could survive and float on the "surface" of the sun? Does the sun even have a surface? Is there a laser powerful enough to overcome all of the electromagnetic radiation from the sun such that you could actually discern it's signal? Not pedantically, I stand by my assertion that it cannot be directly measured.