How about a login when people use the chat function from the website for webbot. Say:

Username: Xtreme
Password: blah
Message: Sup guys

Then the display on battlenet is like

Webbot: Xtreme says: Sup guys

And the bot owner is the only one who can setup usernames/passwords for the website chat function.

Good idea? Or is it impossible?

well thats not impossible, because i've seen it done, and are you sure webbot doesn't support this feature? =\

Dave has a script that does it, I think. Ask him for it.

Webbot does support you to use just 1 password, but you don't know who it is if you give the password to a certain amount of people.

Who is Dave and how do I get the script for it?

https://davnit.net/bnet/vL/index.php?action=profile;u=95

This was discussed in another thread, and some code was even provided.  Try searching

Just an example of the system's flexibility, it is possible to configure your Webbot to allow only certain forum members access to chatting on Webbot, and it could show their forum name, without ever giving anyone the Webchat password.