I am not sure why do you want to save values in hidden question first. I am pretty sure, it is possible using those variable directly in constructed list.
Anyway for your help, here is the method.
You need to create free format question, let's say question name is "Dummy". You need to define variable name in variable/question html tab. Let's say, we have created Dummy_r1, Dummy_r2.
Now to save value of any quesiton( I am assuming Q1 as multiselect). Here is the code, you need to write in html section.
<input name="Dummy_r1" id="Dummy_r1" type="hidden" value="[%Begin Unverified Perl
Let me know if it is not clear to you.