Your best bet is not to try and sculpt the mesh directly. Create an EXR vector displacement map and sculpt using that. The micro poly displacement at render should take care of the underlying mesh displacement and shouldn't have any trouble if you have an even mesh as Michael suggested. The advantage of using an image is that you could re-import your MoI model (if you make some changes), and reapply the displacement very quickly. However, you need to UV map the mesh before you can use image based sculpting. Vector displacement maps allow not just height data but side to side as well so you can sculpt cavities and overhangs. Modo 501 also has multi res sculpting but the base mesh must be Catmull-Clarke subdivided before you start, so it won't play well with a MOI mesh.

The time consuming bit is UVing the mesh, but if you use the Atlas option with the UV projection tool, it should be good enough and is very quick. If you get problems with seams, you might have to take a different approach.

Here is a quick example. This is a glass bottle modeled in MOI. The first image is with the vector displacement map and the second is without it.