No, the only two ways you can do it are the two you mentioned, though I don't think you're understanding mesh colliders correctly. People often create entire levels in 3D modeling programs, and then import them with mesh colliders on them, and the games run just fine (I'm talking about potentially tens of thousands of verts on a single model, here).
I remember 3DS Max had an Optimize feature that would drastically lower the polycount of the model without sacrificing quality. Perhaps Maya has something similar you could look for, but again, I wouldn't worry about your model. Just import it and put a mesh collider on it.
Sidenote: Saying something has a "huge polycount" isn't helpful... what is helpful would be to post the model statistics, saying exactly how many tris/verts the model has, and even posting a picture of it.