Multiple choice: track individual selected choices in piped text

I have looked at various options on how to deal with this challenge, but I cannot seem to find a solution.
Here goed the challenge, in a nutshell: for an experimental design, we first ask respondents to indicate, in a multiple choice question, which four (out of eight) options they would prefer. We then need to track the four selected options in four metadata fields (selected1, selected2, selected3, selected4), and the same for four non selected options (nonselected1, nonselected2, nonselected3, nonselected4), which we can then use in the experimental stimulus to systematically vary the number of (non)selected options that were approved.
Qualtrics piped text only allows me to obtain a single comma separated string of the selected options in the multiple choice question, but does not allow me to separate out the individual options that were selected into separate metadata fields. I have tried experimenting with the syntax (i.e. ${q://QID1/ChoiceGroup/SelectedChoices/1}, ${q://QID1/ChoiceGroup/SelectedChoices{1,1}}, ${q://QID1/ChoiceGroup/SelectedChoices//1} to try and reference individual items in the comma separated list, but to no avail.
Any help would be much appreciated.