I’d say the biggest tip would be to balance your exposure so you didn’t have the crushed blacks in the first place. Especially on cameras like the 5Dmkii and 7d, if you are crushing blacks in production, it is going to be near impossible to pull that information back out of the image, because it simply gets lost between the lack of 4:2:2 color space and the compression codec. These cameras do get contrasty really fast, but making sure the light in your scene compensates for that should solve most of your problem.
These cameras aren’t shooting in any type of raw format for video (such as Red’s do), but go straight to a compression codec. Thus, image degradation.
As far as working with the footage you’ve got using only the FCP 3-way, I would say increase the black levels slightly (only by a few points), and the same with the mids. Unfortunately when you try to get back that information that is already lost, you are going to introduce more noise into the image, so you may be (mostly) stuck with what you’ve got.
You could always PM me (arstewart AT gmail.com) with a link to a short sample of the footage in question, I can download it, use the 3-way in FCP and email you the FCP project back so you can use the 3-way settings I come up with. That may give you something to start with for the rest of your footage.
Aaron R. Stewart
arstewart@gmail.com