Then parent your mesh to this curve. Set your meshes display detail to be bounding box only in it's object display override. Then save this file. Heres how I did it for a pine tree http://x019.uploaderx.net/x/080_psuedo-proxy.gif (http://bayimg.com/kaGgJaABo)
Open your real scene and reference in the file. The interesting thing is that it seems that due to the way maya handles references. It can tell it doesn't need to recurse through the whole mesh data and it just pulls in your bounding box and curve information. Because it loads the file as a reference way faster than just straight up importing it.
Once referenced, just select the curve, instance it around and there ya go, great method to place trees and such. Used it to do this render http://x021.uploaderx.net/x/046_renderB.jpg and will use in the future!
although it appears that in maya 2008, MR 3.6 has the ability to use some kind of 'assembly' object that seems like it's intended to function like a proxy object... so this might be useless