One of the people on another board that I frequent has used Hydrogen Peroxide with great success to remove BBA from his plants. He treated them outside of the aquarium and rinsed them afterwards to help prevent getting too much H2O2 in the tank. Some plants were much more tolerant of the treatment than others. He dipped the main plant but not the roots.
If you decide to try this, keep in mind that it is a short term solution and to keep the algae from coming back you will need to get the nutrients in your tank balanced.