The bus from Split should stop at the begining of Peljesac peninsula (where the road to Ston starts). Since I am not sure if the bus will go all the way to Ston I will try to contact the Bus Terminal.
Unfortunately, I am abroad at the moment, you will receive an answer till the end of this month.
Admin
P.S The "transportation by buss" section will also be updated with timetables and other useful info soon...