In freeport once you get past the guards and into the bank you can stand behind the wall and swing the camera to target the banker and bank. You don't need to be FD or sneaking, no mobs can see you and bankers will deal with you even when your KOS. You can FD to be extra careful but it's not required.
When you go into the bank you walk in the door and are immediately facing a wall, it's that wall you have to use. If you stand there for a few mins you'll more than likely see someone else doing it. Just make sure you don't go around the corner. Both bankers will aggro and the vendor and guard will assist.
Also if you use the tunnels and aren't extremely unlucky a lot of times you can make it to the bank only aggroing 1 or 2 guards, they are Paladins though so be careful FDing with them casting
edit: forgot to mention, you can get your NFP faction up so you're not KOS with NFP guards but still KOS with the bankers by turning in 2 gold at a time in EFP for the
Fabian's Strings quest. You can get a wolf form or invis to get into position but once it wears off you can Sneak and avoid aggro from the guards on both sides of you. Think it took me an hour or two and maybe 200pp in gold to get to Apprehensive as an iksar monk, but it's been a while.