(Unity3.3 standard)How to CombineChildren and keep Dynamic Batching?

My project is using thousents of instatiated objects. When I combine children in my prefabs and combined mesh have more than 300 verts (and it usualy have) Unity is not able to batch them. :( That behavior leeds to big performance loose. Is there a way or script that will keep meshes at batchable size or way to batch bigger meshes?