in time of famine

Last year, I grappled with the question of Yitzchak and Rivka not abstaining from marital relations during a famine when Yosef is said to have done so. Alas the KallahMagazine blog posts of last year have been obliterated from existence. But the Divrei Chaim did pick up on the issue, as you can see here: http://divreichaim.blogspot.com/2007/11/status-of-avos-as-bnei-noach-or.html
During this year's layning of Parashas Toldos, I thought of another possible explanation, though it would have to rely on the principle of events presented out of strict chronological order. During the famine, Yitzchak and his family travel to Gerrar, as Hashem told him not to leave Eretz Yisrael. Just like his father had, Yitzchak tells the people of the region that his good-looking wife is his sister. The difference is that whereas Sarah was instantly taken for the king -- both in Egypt and in Gerrar -- this king is more cautious. He allows many days to pass and seems to keep the purported brother and sister under observation until he espies behavior between the two that indicates they were not in fact siblings. : "vehinei Yitzchak metzachek es Rifka ishto" (26:8). This leads to Avimelech's "Gotcha" charge of Yitzchak. But the king accepts Yitzchak's explanation of his actions and lends his protection to the couple by decreeing death on anyone who dare touch them (26:9-11).
It is the following verse that relates Yitzchak's successful harvest. So I would venture to say that given the fact that much time is said to have lapsed before Yitzchak dared to be intimate with his wife, it may have occurred only after his harvest. The blessing evidenced by the abundance of wheat that he reaped may have indicated to him that they were no longer in the midst of famine and so that it was permissible to resume marital relations, particularly as he had not yet fulfilled pirya verivya with no daughters.