Automatic savings account using 2 wallets?
I answered my own question.

I used the following PHP code...

$savings = 0.001;
$txfee = 0.0001;
$amount = floatval(($bitcoind->getbalance() - $savings) - $txfee); // getbalance() returns 0.005
$outputAddr = [
    '1GAnaq3atnKkxFsUC4Vky8Ysb751LbxHSC' => $amount, // wallet 1 address
    '122ExHr92bEgJbepSHmQCruCRR3YRR6dx5' => $savings // wallet 2 address
];

$rawtxUnspent = [];
$unspent = $bitcoind->listunspent();
foreach($unspent as $tx) {
    array_push($rawtxUnspent, [
        'txid' => $tx['txid'],
        'vout' => $tx['vout']
    ]);
}

$rawtx = $bitcoind->createrawtransaction($rawtxUnspent, $outputAddr);
$signedtx = $bitcoind->signrawtransaction($rawtx);
$senttx = $bitcoind->sendrawtransaction($signedtx['hex']);

$senttx === false ? print $bitcoind->error : var_dump($senttx);


and got this output...

string(64) "bae6d6978da7a50422a943ac42017c64478169ce87a264d7cedbaa5a869558b4"

The transaction is confirmed and worked exactly as I hoped. :)

https://blockchain.info/tx/bae6d6978da7a50422a943ac42017c64478169ce87a264d7cedbaa5a869558b4