I'm not quite sure about proFTPD, been using FlashFXP. Maybe they works the same, i don't need to enable anything to FXP, there's and option to choose on each display to switch between FTP browser and Local browser. If one side is set to Local and the other to FTP, it mean it's FTP mode. But if both sides are switch to FTP mode, then you can login to both servers and transfer files from there.
Maybe you can try to look out for the "switch to FTP" option on the file display column of proFTPD. Hope it helps.