You definitely need something to supplement the primarily landscape tools you mentioned. You do have to spend time on any tool to really figure out what it can do. Poser also is specialized and as stated can work with it, however you really need a plugin for good support. C3 really needs landscape help so those programs should help. It contains modeling features that should fill in gaps with those programs. Since someone else bought it for you it is certainly worth your time to see what it can do.

No need to think outside the box....
    Just make it invisible.