He probably was blowing this problem way out of proportion,
Lois: No, I definantely want to make love with Clark.
and it wouldn’t even be an issue. After an afternoon of making out with him, which Clark would sacrifice for the good of the cause, Lois would calm down, right?
Lois:

Just keep thinking that Clark. Just come back to me and make out some more, now. Hmm, better yet, let me start getting ready for your return.
She would know that Clark wasn’t going to dump her, so she would stop freaking out, and they could return to dating as normal. Right? Therefore, he only needed to make it through the afternoon.
Lois: Normal dating? What does he mean by that? We havn't gone on a date in months and have been doing intense, heated makeout for a while. What would that mean normal dating would entail?
Clark could do this. He could, somehow, not move their relationship any further forward for one afternoon, right?
Lois:

You can keep going all night long. Let's get going.