That's how my extension works, except it has other very useful features and fields used specifically for web directories.
I am also using roboform only It has an awesome autofill feature for a profile I just visit directory->submit.php and iRoboform automatically fills it and I have to only click the submit button!
I do it myself. I look for the directories that seem reliable to me and have free no reciprocal and no account submission. I don't waste time with the others.