I found a workaround: I contacted the developer of the lightmapping shader and got this response:
"First of all, thank you so much for buying Standard Plus.
I'm making a video tutorial on how to get only the lighting information from Corona, since out of the box they still don't support that, as opposed to V-Ray.
But it's not difficult. The way you achieve that is by creating a Corona material called Corona RaySwitch Material.
In the Rayswitch material you'll have four material slots: one for global illumination, one for reflection, another for refraction, and another one for the visual material for the camera.
So, in the first three slots, you plug the material you created for your object.
But in the last slot, the visual material, you put a 100% white material, with no reflection or refraction.
Now, you assign this Rayswitch material to your object and in the Render to Texture you simply choose Corona Beauty, just like that.
What will happen is, since for the camera the material is 100% white, the render will behave like it is rendering only the lighting coming to the object, but thanks to the rayswitching, your material will spill the GI colors to other materials, and all the reflective properties wil be preserved to every other object that come in contact to it."
For anyone doing a search for lightmapping. It's not ideal if you have many materials, but it's a lot better than nothing.