I'm sorry, but it's a bad idea. This way, Yoda is no longer a surprise Jedi Master in ESB (although watching the prequels first would spoil this anyway), he's only in exile for two years, and there's no explanation for wherever the hell he was for the 20 years between III and IV. And anyone watching that scene in ANH for the first time would be thinking something along the lines of WHAT THE FUCK?! for the rest of the film.