The two scripts are almost identical. Actually the only difference is the action the shell script should call (add or remove). The rest of the scripts are completely the same.

I call this file addhost.

using terms from application "Quicksilver"
	on process text txt
		set the_password to "YOURPASSWORD"
		repeat with delimiter_position from 1 to (length of txt)
			if character delimiter_position of txt = " " then exit repeat
		end repeat
		if delimiter_position = (length of txt) then
			set hostname to txt as string
			set ipaddress to ""
		else
			set hostname to characters 1 thru (delimiter_position - 1) of txt as string
			set ipaddress to characters (delimiter_position + 1) thru (length of txt) of txt as string

		end if

		do shell script "sudo hosts.sh add " & hostname & " " & ipaddress password the_password with administrator privileges

		return nothing
	end process text
end using terms from

I call this file removehost.

using terms from application "Quicksilver"
	on process text txt
		set the_password to "YOURPASSWORD"
		repeat with delimiter_position from 1 to (length of txt)
			if character delimiter_position of txt = " " then exit repeat
		end repeat
		if delimiter_position = (length of txt) then
			set hostname to txt as string
			set ipaddress to ""
		else
			set hostname to characters 1 thru (delimiter_position - 1) of txt as string
			set ipaddress to characters (delimiter_position + 1) thru (length of txt) of txt as string

		end if

		do shell script "sudo hosts.sh remove " & hostname & " " & ipaddress password the_password with administrator privileges

		return nothing
	end process text
end using terms from

Now I am able to create a local domain by opening Quicksilver (double-control in my case) press period, write the domain name, press tab, and select the addhost action (ad is enough in my case). Removing is just as easy – the last step is just to select the removehost action (re is enough in my case).