Network Utility Maximization (NUM) is a well accepted theoretical framework that describes how congestion controls cooperate to achieve an ideal sending rate allocation, for given utility functions of senders and constraints of the network. These network constraints are expressed as a "cost'' in the framework. In practice, most congestion control mechanisms obtain feedback that is different from the framework's "cost''. This paper focuses on Explicit Congestion Notification (ECN), which has been shown to be advantageous when it is available, e.g. with the popular Datacenter TCP (DCTCP) mechanism. However, different from the framework's cost, ECN marks are not additive. We present a practical solution to this problem. Our solution changes how end hosts interpret the ECN signal, while for the router side, a special configuration of RED is used.