Nowadays, the wireless local-area network (WLAN) has been deployed everywhere as a common access medium to the Internet. In WLAN, the network configuration should be optimized according to traffic demands and network environments which will change dynamically. Therefore, we have studied the active AP configuration algorithm for the elastic WLAN system to achieve the elasticity of WLAN. However, this algorithm requires a long CPU time in the large search space when numerous APs are deployed in the field. In this paper, we propose a preprocessing stage for the AP configuration algorithm to reduce the CPU time by limiting the number of APs in advance. Both the exhaustive and heuristic approaches are adopted, where either one should be used depending on the network topology. Through extensive simulations using the WIMNET simulator, the effectiveness of the proposal is verified.