This is a custom solution that uses hook_form_alter() to prepopulate the Ubercart Address field with fields from the logged in user's Content Profile.

<?php
/*
  * Implementation of hook_form_alter()
  * populate address field on ubercart checkout using 
  * user's content profile
  */
function grasmash_form_alter(&$form, &$form_state, $form_id) {
  if ($form_id == 'uc_cart_checkout_form') { 
    //load user and profile objects
    global $user;
    $profile = content_profile_load('employee_profile', $user->uid);

    //map source fields in content_profile to target fields on checkout form
    $field_matches = array (
      'billing_first_name' => $profile->field_first_name[0]['value'],
      'billing_last_name' => $profile->field_last_name[0]['value'],
      // 'billing_company' => NULL,
      'billing_street1' => $profile->field_employee_location[0]['street'],
      'billing_street2' => $profile->field_employee_location[0]['additional'],
      'billing_city' => $profile->field_employee_location[0]['city'],
      'billing_country' => $profile->field_employee_location[0]['country'],
      'billing_zone' => $profile->field_employee_location[0]['province_name'],
      'billing_postal_code' => $profile->field_employee_location[0]['postal_code'],
      'billing_phone' => $profile->field_employee_location[0]['phone'],
    );        

    //set default values
    foreach ($field_matches as $target_field => $source) {

      if ($source) {

        /* select list needs to be set differently
        determine appropriate target field key for source value */
        if ($target_field == 'billing_zone' || $target_field == 'billing_country') {
          foreach ($form['panes']['billing'][$target_field]['#options'] as $key => $value) {
            if ($source == $value) {
              $form['panes']['billing'][$target_field]['#value'] = $key;
            }
          }
        }

        //set values for normal text fields
        else {
          $form['panes']['billing'][$target_field]['#default_value'] = $source;
        }

      }
    }
  }
}
?>

You'll clearly need to change the mapping array to match your specific field names.

Note: If I were to do this again, I'd consider using the Ubercart Addresses module with the following plan:

• Set Ubercart Addresses to not require address on registration
• Set Content Profile to require an address CCK field on registration
• create custom module with hook_form_alter()
• have hook_form_alter() add a new submit handler for the user_registration form
• have submit handler use values provided to CCK address fields to create a new db entry in the uc_addresses table