This CodeLet alter the 'uc_paypal_wps_email' variable when PayPal payment is enabled with Ubercart & sets to node author's PayPal account email address. This requires creating a field on user's account with name 'PayPal Email' (field_paypal_email).

CodeLet
<?php
/**
 * @file
 *
 * @author DrupalD
 */

/**
 * Implementation of hook_form_alter
 *
 * @param unknown $form
 * @param unknown $form_state
 * @param unknown $form_id
 * @author DrupalD
 */
function mymodule_tweaks_form_alter(&$form, &$form_state, $form_id) {
    if (
$form_id == 'uc_paypal_wps_form') {
       
$am__cart = array_values(uc_cart_get_contents());
       
$sn__uid = $am__cart[0]->uid;
       
$am__paypal = db_select('field_data_field_paypal_email', 'ppe')
                    ->
fields('ppe', array('field_paypal_email_email'))
                    ->
condition('entity_id', $sn__uid, '=')
                    ->
execute()
                    ->
fetchAssoc();
       
$form['business']['#value'] = $am__paypal['field_paypal_email_email'];

       
//When testing paypal  as buyer. DO NOT REMOVE comments unless you are testing paypal.
//         $form['email']['#value']  .= '-buyer';
   
}
}
?>
Info file details
name = Ubercart Tweaks
description = Tweaks for Touristing website. Built by <a href="http://bit.ly/1N7nWf0">Drupal Developer</a>.
dependencies[] = uc_paypal
package = DrupalD
core = 7.x
Compatibility
Submitted by DrupalD on