How do I create a string that is a concatenation of labels, and then use that string to reference a list?

I have a constructed list containing the members chosen in a previous multiple-select question. I want to concatenate the labels of all the members in this constructed list to create a string. And then I would like to use the string to identify another list to ADD to a constructed list.

As an example...
Labels of Members of First Constructed List 'Q1ListChosen':
A
B
C

Concatenation of Labels:
ABC

So far I have tried this...

ADD(FormatListLables(Q1ListChosen, "", ""))

and also variations on this...

Begin Unverified Perl
my $stringListName = FORMATLISTLABELS(Q1ListChosen, "", "");
ADD($stringListName);
End Unverified

Both generate errors, a data type error with the first code snippet and script error #132 with the second snippet.

Any thoughts on how I can accomplish this?