I put this in as a system hi ticket and the following was recommended:
function group_members(){
var answer = new Array();
var group = current.variables.variable_name_for_group_reference;
var group_members = new GlideRecord('sys_user_grmember');
group_members.addQuery('group',group);
group_members.query();

while(group_members.next()){
answers.push(group_members.user.toString();
}

return 'sys_idIN' + answer.join();
}
It worked in our instance. We eventually were able to get both versions working.