If you have a house that has dinner, I would suggest hosting a sorority for dinner once a month and go all out--get dressed in shirts and ties, have your advisor welcome them, escort the ladies to their chairs and seat them etc. Learn and practice formal etiquette and dining skills--this is important for career prep, but women tend to dig it when a man can display his charm and skills.
If you don't have a house, see if the campus food services will cater such an event (possibly for free if you tie in the educational element of etiquette training) or maybe an alum will host you at their home or ranch.
Serenading is a good idea, too.
Hold joint new member/pledge education events with the sororities. The new members will enjoy the opportunity to do things with other groups.
Hayrides are fun too.