See, that's the trick: He doesn't have to sign anything he disagrees with.
I know that it is not uncommon for Congress to send "poison pills" to the President (whoever it happens to be at the time). Bush the Younger got many from Congress, and he wasn't the first. He won't be the last. It's one of the reasons I favor giving the President some form of line-item VETO power. If there's a reason he doesn't like a bill, he can go on record as not liking a portion by striking it and send it back to Congress to re-consider.
Better yet, I would like to see some responsibility in Congress. Something that requires "riders" to a bill actually be related to the bill would be nice. "But that's the only way some things can get passed," I hear someone say. My reply is, "Yeah. Do you suppose there might be a reason for that?"
It would also be nice if Congress would spend more time reviewing laws that have been on the books for a while and consider repealing those that are deemed to be no longer relevant. I would rather they do that than sit around wondering what else they could do to micromanage my life.