A question for scenebuilders / screenshot artists

To be clear, this is NOT a technical help thread. I just want to know, for those of you who still do scenebuilding and postprocess and whatnot with Garry’s Mod screenshots, is there any feasible way for me to simulate SSAO (ambient occlusion) in post? Like, any technique for faking it in Photoshop or GIMP that looks good? Nvidia’s driver-enforced SSAO used to work in-engine, but now it doesn’t and I can’t for the life of me figure out why, so I’m going to need to do AO in post unless they get around to fixing it.

I had no idea where to post this since it isn’t a technical support question, isn’t a dev question, isn’t art, and isn’t a suggestion. Can anyone lend me a hand here? I really don’t want to have to learn to work with SFM on short notice JUST to get in-engine SSAO back.