Brifters? No, unfortunately, brifters will not shift a mountain front derailleur. The levers will not pull enough cable to actuate the front derailleur across all three of the rings.
I like the idea proposed by waynemyer and DaveB: a Sugino triple. Something like an XD2/XD600 is available with 24/36/48 or 24/36/46 rings, is 9 speed compatible, and will run on a Shimano UN54 or UN55 bottom bracket. It might even shift with your current front derailleur. If not, a Tiagra triple front derailleur, which is more tolerant of smaller rings than the Ultegra, should get the job done.
If you still need lower gearing, your next stop will be the cassette. A larger range cassette might, however, require a longer cage derailleur. Something like a 9 speed Deore will probably work just fine and will play nicely with your brifter (same cable-pull ratio). Shimano rear mechs typically come in three flavors: short cage (road), GS (medium length cage), and SGS (long cage). If you have the choice, get the long cage. It will weigh just a bit more and require a very slightly longer chain, but will leave you the flexibility to run just about any gearing that you desire. In any case, stay clear of 10 speed DynaSys rear derailleurs. They use a different cable-pull ratio than 9 speed rear derailleurs and will not work with your brifters.
Sorry to take you yet another level down into the rabbit hole. Changing gearing sometimes opens Shimano's Box; altering one part of the system often leads to a seemingly endless chain of modifications necessary to make the whole mess work properly. Having a good LBS with whom you can work is a great asset, as, for instance, they might be able to experiment with different spindle length bottom brackets at no extra charge to you (although you will probably end up with either a 110 or 113mm spindle) in order to ensure that your drivetrain is set up with the proper chainline.