not able to customize Contribution tokens

[haggertypat]

I'm trying to customize the contribution.receipt_date token with help from https://civicrm.org/blogs/colemanw/create-your-own-tokens-fun-and-profit.

I cannot seem to update the contribution values or even access the contribution tokens or values from the "civicrm_tokenValues" hook.

function MyModule_civicrm_tokenValues(&$values, $cids, $job = null, $tokens = array(), $context = null) {
    print_r($tokens); // contribution tokens are not listed
    print_r($values); // only contact values are listed
}

Blindly attempting to just set a value for the token doesn't work either, the default value is still used:

function MyModule_civicrm_tokenValues(&$values, $cids, $job = null, $tokens = array(), $context = null) {
    foreach ($cids as $cid) {
       $values[$cid]['contribution.receipt_date'] = 'test';
       $values[$cid]['receipt_date'] = 'test';
       $values[$cid]['contribution'][0] = 'test';
       $values[$cid]['contribution']['receipt_date'] = 'test';
    }
}

Is there some other hook I should be using? Any other ideas? Thanks!