I have some friendly advice for all my good friends who are currently competing for the Republican nomination for president: you should refuse to sign pledges. Sure, the first one seems harmless. Maybe it's a pledge not to raise taxes. No problem. Then the next one is a pledge to oppose gay marriage. OK, you can do that too, even if you'd rather not. But then the next one is something like this. And you're stuck. You can't pretend to have a principled objection to pledges, but you're toast with the tea party crowd if you refuse to sign because you disagree with parts of it. These folks accept no shilly shallying from politicians with "nuanced" views.
So your best bet is to simply register a broad objection to presidents signing interest group pledges at all, along with a noble-sounding statement that you want people to judge you by your past actions and character etc. etc., not by who can out-pledge the other. Just say no to pledges.