If I have assumed correctly, you could create a constructed list as follows ...
Begin Unverified Perl
You will need to create a pass-in sample field (I called it SampleGroup) that has half your sample tagged as "1" and the other half tagged as a "2". Define this sample field as a whole number data type. Import your sample in with this sample field included.
In my constructed list example above, change "Q1List" to your list name.
When SampleGroup=1, the respondent will see 1-2-3-4 displayed.
When SampleGroup=2, the respondent will see 4-3-2-1 displayed.
When you reach the analysis stage, you can use SampleGroup as the identifier to the order in which the respondent was displayed the code list.