You can do this, but in my opinion it is better to do it in steps. If you blast straight into EtOH, it may be difficult to visually tell when most of the butane has evaporated. Then you may be sticking a container of EtOH mixed with butane into the freezer, where the butane will remain a liquid and may surprise you the next day. What I like to do is blast into a container until I see the butane almost all gone (gooey 'tane soup stage), then pour in EtOH heated on a double boiler for a quick "purge." EtOH boils at ~78C while butane boils at -1C so I believe this should almost immediately get rid of most of the remaining butane.