cmd takes an optional second argument that is a string that contains stdin. Perhaps that will work for you? I haven't tested this, but I thought i'd throw out the possibility since there are not any other replies.

$stdin  = "first name\n";
$stdin .= "middle name\n";
$stdin .= "last name\n";

($out, $err, $exit) = $ssh->cmd($cmd, $stdin);
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Brad