About an hour ago I would have replied saying that just isn't possible without the max plugin, but a thought occured to me. In all my previous experiments into the matter, PCS hasn't been able to convert any model with more than about 12-15k polys. However, I just got a 230 000 poly model in-game using it. We're talking a 60 meg POF file here! It was murder on framerates, but it worked.
230k probably isn't even the max the engine can take either. I just got sick of the 4 minute conversion times.
The trick is, you need to separate the model into separate submodels for conversion via PCS. My test model was 60 spheres of 3840 polys each, but it should be able to take submodels with polycounts around that 12-15k mark. So, you could try splitting it into 10 separate ~12 000 poly submodels.
The other cool thing with this is that it sets your model up nicely to implement detail box techniques to prevent ALL those polys being drawn at once, murdering framerates. You should definitely do this in this case considering how large the land mesh will be.
