Adaptive CBC exercises are difficult to modify and have it reflected correctly in the analysis. Like Zach said, you can put in code to hide the none options but the designer will still think it showed these none options in the must have or unacceptable questions. How often did the none options appear in the must have or unacceptable questions when you went through the survey like a real respondent? If you have enough screener tasks, I wonder if the respondent marked concepts that included none as a possibility.
The exercise tries to be smart by identifying levels that are common in your acceptable choices. If the none was common in the acceptable concepts, why would it be bad for them to appear in the must-have and unacceptable questions? Would only bad respondents choose the none option in the must-have and unacceptable questions? I can see why you would want to save the respondents time by excluding these from the must have or unacceptable questions.