Thats not possible due to the way FlashFXP is setup to handle a blank ip. As per-request by many FlashFXP users, if the ip address is blank FlashFXP tries connecting to the site entry name.
Ok- I was doing some reviewing of my source code and it appears this is no logner the case. Apparently that idea caused problems and was removed ages ago. Even though it was removed there was a bug in the site manager that allowed connections to connect to the site name. Connecting via the connect button didn't work.
Inlight of this new news, I will add a prompt which prompts for a host address when one is not entered.