secret seed is "erupt consider beyond twist bike enroll you salute weasel emerge divert hundred"

with keystore password "password"
with hdPath = "m/44'/60'/0'"

the private key that is returned is a 62 character hex value.

example code:
(using lightwallet.keystore.deriveKeyFromPassword(password, function(err, pwDerivedKey))

var keystore = new lightwallet.keystore(secretSeed, pwDerivedKey);
var hdPath = "m/44'/60'/0'"; //as defined in SLIP44

keystore.addHdDerivationPath(hdPath, pwDerivedKey, {curve: 'secp256k1', purpose: 'sign'});
keystore.generateNewAddress(pwDerivedKey, 1, hdPath); //Generate a new address

var incompleteAddress = keystore.getAddresses(hdPath)[0];
keystore.setDefaultHdDerivationPath(hdPath);
var hexSeedETH = keystore.exportPrivateKey(incompleteAddress, pwDerivedKey);

..

hexSeedETH.length = 62.

something like a:

function pad(num, size) {
var s = num+"";
while (s.length < size) {
s = "0" + s;
}
return s;
}

with a:

hexSeedETH = pad(hexSeedETH, 64);

returns valid private keys that can sign for this address for the ethereumjs-tx module, and this library's signtx function.