George Lucas should have just changed the subtitles in the scene back to what it was in the original script:

In the released version, Greedo says "I've been looking forward to this for a long time."

In the original script, he says "I've been looking forward to KILLING you for a long time."

I don't know what more reason Han could have had for shooting Greedo.

If Lucas simply replaced the line, he would provide total justification for Han shooting, without having ILM spends weeks working on the shot that STILL looks awful.