Alright, I've got a working prototype of how I would tackle this.

I'd start by adding the select questions to the same page, somewhere before the free format question. I added one for each possible column of the table and gave them all shared base name with an iterator at the end: \"CustomDropdown1,\" \"CustomDropdown2,\" etc.

In the free format question, I added \"multiSelectWrapper\" elements where I wanted the dropdowns to end up in the table:


<tr>
\t<td>
\t\t<div class=\"multiSelectWrapper\"></div>
\t</td>
\t<td>
\t\t<div class=\"multiSelectWrapper\"></div>
\t</td>
\t<td>
\t\t<div class=\"multiSelectWrapper\"></div>
\t</td>
</tr>

Then I gave the free format question this script:

[js]
<script>
$(document).ready(function(){
\t// Settings
\tvar customDropdownBasename = 'CustomDropdown';
\t
\t// Run
\tvar wrappers = $('.multiSelectWrapper');
\tfor (var i = 0; i < wrappers.length; i++) {
\t\tvar customDropdownQuestion = customDropdownBasename + (i + 1);
\t\t$('#' + customDropdownQuestion + '_div').hide();
\t\t$(wrappers).eq(i).append($('#' + customDropdownQuestion + '_customdropdown'));
\t}
})
</script>
[/js]

and this custom verification:

[js]
// Settings
var customDropdownBasename = 'CustomDropdown';
var clist = [% ListValuesArray(list1) %];
var errorMessage = 'Error...';

// Run
clist.forEach(function(quest){
\tvar qname = customDropdownBasename + quest;
\tvar checks = 0;
\t$('input[name=\"hid_list_' + qname + '\"]').val().split(',').forEach(function(item){
\t\tif (SSI_GetValue(qname + '_' + item)) {
\t\t\tchecks++;
\t\t}
\t});
\tif (!checks) {
\t\tstrErrorMessage = errorMessage;
\t}
});
[/js]

where \"list1\" is the name of the constructed list that controls which columns are shown.

Free Format - items in the combo box