Scott said in one of his books that he really didn't think the giant cucumber storyline was as funny as he thought it would be, but he was working his day job at Pacific Bell at the time and couldn't afford to throw it out, so he just told the truth.
"Obviously that was the whole idea from the start, otherwise he would have just drawn a new first panel and moved on."
I disagree. I have never seen this guy abandon an idea. They all seem to come to resolution, even if it is absurd and immediately disregarded. It's quite probable that Adams didn't want to continue this idea and panel 2 was an easy out.