Scripting large amounts of tree instances

First off let me explain what I am currently working on. I am creating a large terrain purely based off data sets given to me by my instructor. So the terrain is 100% created from the data set, I cannot use the terrain place trees or paint detail options in the terrain builder. This being said, I need to generate a large amount of shrubs (mainly sage brush). I cannot do this by creating an instance everywhere I need a shrub placed because it takes forever to compile. Is it possible ,and if so how can it be done, to create a mesh of say 100 shrubs and use this mesh to place at a particular tree instance.

All of this must be done in a script.

Thanks for any response I have spent too many hours trying to figure out a solution to this problem.