I've just tried something I was thinking about for a long time now. I don't know, maybe this trick is well-known for most of you, but I personally haven't seen it used in any map. So whatever, here's a pic of the whole deal:
Faked bumpmapping in Goldsource with additive render mode. I think it looks neat, I'll try it in my upcoming map(s), if I'll have the nerve to actually finish a map
looks good though :]