That's a great idea. Better than what I can up with, probably:
As Obi-Wan opens the box, he says (taken from a bit later), "Your father's lightsaber. Your uncle..". Then when Luke asks what it is, "It is the weapon of a Jedi Knight.."}
Also thought of a few small ESB changes. Obi-Wan could say that Yoda was A, not THE, Jedi who instructed him. Later his voice-over could be "Was I any different.." (removing "when you trained me.") And Yoda could say "For 800 years I trained Younglings."