I have had other 2M ARFs that I built the wing as a two piece. They have been very successful as EP gliders. (Not as much stress on the wing with EP launches.)
I think it is important to insure the joiner is a snug fit in both joiner boxes. I build up the joiner with balsa to insure no movement is possible as required. I then epoxy one end of the joiner into one wing half. You can't loose/forget the joiner that way and it is definitely a tight fit on that end.
I also make a locating pin as mentioned above.
I then use tape to hold the wing together during flight.