Elegant way to project textures on a terrain

i have a terrain. and i use 4 texture units, so i guess i have none free for projectedtextureutil. is there an efficient way to project stuff on my terrain without using a second renderpass just for my projections? i need this to mark specific points on my terrain like it's done in warcraft 3 when choosing a target for a spell

This thing is discussed here.


I have this in my bookmarks… because I, for sure, will need it.