Forgive me if I'm wrong. But couldn't you use an info_texlight, then smart edit the key to be the name of the texture, and the value the color of the light?
So lets say I wanted to light up a sign and the sign's texture is "C1A1SIGN2B", and I also want to give it a yellow tinted light.
Create info_texlight
Smart Edit
The Key would be name of the texture
The Value would be the color of the light, so for example : 126 126 63 200
The end result would look something like the sign in this picture (taken from my own map) Each texture that shares the same name will light up in the same value. Just make sure you're only adding the lights to the textures you want, and not the entire lamp. Also, a useful note: You can add multiple keys/values to an info_texlight. So you can use one info_texlight for multiple objects. I hope this helps.