If you have a perl script that just performs the backup you could just "system" the script in background

#!/usr/bin/perl -w

use strict;
use CGI;

my $page = new CGI;

print $page->header();
print $page->start_html();
my $command = qq(script/that_performs/the/basckup.pl &);
system ($command);
print qq(Finished);
print $page->end_html();
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Hope this helps.