I would think your idea is correct. A small gap in the bottom plane should not change the impedance significantly since there is still a solid plane in the top layer. 1mm gap should be wide enough to let three 0.07mm tracks to go through.
Of course you should use enough GND vias to connect the planes in top and bottom layer together, especially along the both sides of the gap.
In addition you have an IMN there, the little distortion caused by the gap could be easily remedied by the IMN. If you are really worried, Vfone's method is a very good solution. Use big 0R resistors as bridges for the LED signals. Place a wide enough GND track in the bottom layer underneath the RF track to function as the reference plane. Three~five times of the dielectric material height is sufficient.