I've used the baking soda trick. I usually fill the gap with liquid glue then sprinkle the soda on and shake off the excess.
Or, spackle the gap/fillet with baking soda first, then add some drops of the thin super glue and it will "wick" through the powder and turn it solid afer it dries.
It's a great way to add strength to T type joints.... a fillet on either side will increase strength by a factor of several times.