Thanks.
I ended up with the following solution for viewing survey results:
Before I open Limesurvey in an Iframe, I use PHP to select the current row in the survey table, modify the token, increase the id and insert the row again, then pointing the viewer to the modified token. Additionaly, I delete previous created "view-only" token rows and also insert the modified token in the token table.
With JQuery I disable all input elements or replace them with their values.
Code:
$('#ls_frame').contents().find("*:not(.submit)").attr("onclick",'');
$('#ls_frame').contents().find(".submit[value='Speichern'],.saveall").hide();
$('#ls_frame').contents().find("#movesubmitbtn").hide();
$('#ls_frame').contents().find("input[type='text']").attr("readonly",true);
$('#ls_frame').contents().find("input[type='radio']:not(:checked)").hide().after('O');
$('#ls_frame').contents().find("input[type='checkbox']:not(:checked)").hide().after('O');
$('#ls_frame').contents().find("input[type='checkbox']:checked").hide().after('X');
$('#ls_frame').contents().find("input[type='radio']:checked").hide().after('X');
Not fully parallel, but it works.