Gist for code at http://obed33.blogspot.com/2016/02/promotion-based-on-payment-method-atg.html

MyCompanyOrderImpl.java

package com.mycompany.commerce.order;
 
import atg.commerce.order.OrderImpl;
import atg.commerce.order.CreditCard;
import atg.commerce.order.GiftCertificate;
import com.sparkred.paypal.PayPalPaymentGroup;
 
 
public class MyCompanyOrderImpl extends OrderImpl {
 
    /** serialVersionUID. */
    private static final long serialVersionUID = -5384547034115301944L;
 
    public String getPaymentType() {
        String paymentType = null;
        for (Object pgObject : getPaymentGroups()) {
            if(pgObject instanceof CreditCard) {
                CreditCard cc = (CreditCard)pgObject;
                paymentType = cc.getCreditCardType();
                break;
            } else if(pgObject instanceof PayPalPaymentGroup) {
                paymentType = "paypal";
                break;
            }  else if(pgObject instanceof GiftCertificate) {
                paymentType = "giftCard";
            }
        }
        return paymentType;
    }
 
}

OrderTools.properties

beanNameToItemDescriptorMap-=\
   atg.commerce.order.OrderImpl=order
beanNameToItemDescriptorMap+=\
   com.mycompany.commerce.order.MyCompanyOrderImpl=order
 
orderTypeClassMap+=\
   shoppingcart=com.mycompany.commerce.order.MyCompanyOrderImpl,\
   default=com.mycompany.commerce.order.MyCompanyOrderImpl