The completely easy way is to reopen STDOUT to your file:

my $outfile = "/home/output.htm";
open STDOUT, ">", $outfile
    or die "Couldn't write to '$outfile': $!";

... rest of the program
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Of course, if your CGI expects some of the CGI specific variables you might need to fake them. If your CGI outputs a status code, you might want to comment that out from your CGI or just munge the created file afterwards.

This trick works because

print "Hello World"
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is secretly

print STDOUT "Hello World";
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