Here's a bit of pseudo-code that I think will work nicely. Note that the use of CGI.pm might not be exactly right, but you should be about to get an idea of what I'm thinking.

print form_start;
# cycle through all the previous hidden fields plus the 
# newest form
for($cgi->param){
    #only pass the fields in %good_fields
    next unless $good_fields{$_};
    #write the good_fields fields into hidden inputs
    print $cgi->input(     -type=>'hidden', 
                    -name=>$_, 
                    -value=>$cgi->param($_));
    }
# print out the next form in the sequence based on the 
# last 'next' hidden field
print get_next_form($cgi->param('next'));
print end_form;
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-caedes