Hmm... I guess it depends on what you mean by flying under the radar, I'm not really sure if you mean they'd blend into military-esque units or the population. I've seen picture of CIA officers in camo and denim, faces painted black.
Also I don't know if you wanted a stand alone figure or a group, if you were going the group route you could have a few SEALs or other spec ops types with the officer and then it's not so much making him blend in but making him stand out- ie instead of full camo maybe give him the standard green uniform without the web belts etc. and instead of a long rifle, maybe have him holding a pistol or something like that.
I think no matter what you're going to have to do some minor modification and kit swapping. The problem is Dragon's Vietnam figure line is OOP and somewhat hard to find.
I'd recommend, if you could get your hands on them, these two figure kits
3302 SEALs (Comes with a silenced pistol btw)
3309 Green Berets
What I like about the Dragon kits is they come with a little bit of everything so if you want to mix and match it's not too difficult, also they're plastic so cutting/scraping/sanding away unwanted detail is much better. Again, they're OOP but you can usually find them somewhere around on the internet.
But this is all with my version of a CIA officer in my head and I'm not really sure what you wanted to represent.