There are no magic "one-size-fits-all" tricks here. But you can design a map in such way. You need to use projection textures and non-shadow-casting lights to sort of "manually lightmap" your level, just like modern game engines would do. This requires a lot of work and design, but it can be done. And what is most important, the lightgem will react correctly, so you don't need any other special hacks to maintain that illusion.
Sounds like shadows should be drawn... But i'm talking about real time soft shadows. Like in modern games