Configure Membership into Web Service

I am developing an windows application (app) with Visual Studio Express 2013. For to log in, the app asks username and password using a form and then consume a method of web service that use a Membership installed into remote DB defined for use in a web site. My trouble is that app is common for any client and web service too, but Membership depend what DB app is pointing at that time. In fact the connection string I pass by parameter and all methods that make sql sentence against DB they know that they have to go. But with Membership is different, because the connection is defined in the web.config of each web site. Are there any way for to make dinamic the assign connection for Membership into the web service ? Thanks in advance