OK, I found a solution. Maybe it's not the best solution but it works.
I just duplicate websocket plugin in C:\Program Files\Construct 2\exporters\html5\plugins\
and in the edittime.js and runtime.js I modified the name and ID from "WebSocket" to "WebSocket2" and "C2WebSocket" to "C2WebSocket2". So every new websocket connection has an own websocket plugin.