Well, you've already gotten the bad news...
Even if by some miracle you managed to glue the roof together perfectly from the inside (which is almost impossible), you'd still see the crack. There's no way to make it disappear without major bodywork, including repainting.
About the only way that's even possible to save this without a repaint is to glue the crack together absolutely as perfectly as you can, then lightly sand the crack on the outside, mask off the rest of the body and spray on a "vinyl roof."