One simple thing you could do, if you don't want to write a plugin, would be to check every tick a variable in the page, or the result of a function in the page. You can call the ExecJS function inside a "System:Compare two values" for example.
More detail example :
I have in my page a function "A" that collects informations to be send to C2. Each time I have to send informations to C2, I call this function, it stores datas.
I have another function "B" that displays this information in a string encoded how it fits me. When this function is called, the stack of informations to be send to C2 will be emptied.
Now in C2, in an EveryTick event, I would start by setting a local variable to the result of the call to the function "B" via an ExecJS. Then, I would read this variable. Explode, JSON decode->put it in an array, whatever fits, and do a for each to treat every action.