You'll need to edit the theme, which means those changes will be lost if/when you update. Not a big deal if you keep track of what you have modified.
The call to display the "un-collapsed" comments is used in the single.php file of your template, since the comments are generally expanded when a post is seen on a single page. What you need to do is copy this call to a function and paste it somwhere in the main loop.
In my theme, based on Thematic Framework, the call for generating and displaying all comments is:
// calling the comments template
I assume the function you need is simply
Now, where to paste it? Well, I don't know. :-)
I tried to find the location. I am pretty sure it is somwhere in content-extension.php, in my theme.. but I could not find more.
PLEASE make a back-up of everything before trying some stunts... :-)