After a little more thorough review of the commerce_paypal_wps module I was able to successfully pass default billing information (name, address, email, etc) from my site to the PayPal site. This is helpful if some users may not already have a PayPal account nor want to create one. In this case when they select the "Pay with a debit or credit card" option on the PayPal payment page all their billing information is defaulted from my site as seen on the checkout/review pages so they do not have to enter it again.

The *commerce_paypal_wps_order_form* function in the commerce_paypal_wps.module creates a hook that you can use:

// Allow modules to alter parameters of the API request.
drupal_alter('commerce_paypal_wps_order_form_data', $data, $order);

In my *hook_commerce_paypal_wps_order_form_data_alter* function (in my custom module) I set the additional billing address fields as described by PayPal at https://developer.paypal.com/webapps/developer/docs/classic/paypal-payme... (in the "Sample HTML Code for Filling Out FORMs Automatically for Buyers" section).

function hook_commerce_paypal_wps_order_form_data_alter(&$data, $order) {
$profile = user_load($order->uid);
$data['first_name'] = $profile->field_first_name['und'][0]['value'];
$data['last_name'] = $profile->field_last_name['und'][0]['value'];
$data['address1'] = $profile->field_address_1['und'][0]['value'];
...
}
Thanks for an extensible commerce_paypal module and I hope this helps someone else.