If your rendering engine can’t use displacement maps, then use it as a bump map instead. Also, some rendering engines (those that only displace points rather than subpixels) work well for medium frequency displacements. With this kind of engine, you can create a displacement map with the fine details to be used as a bump map, and then delete a few of the higher subdivision levels. Now create another displacement map which will be used by your rendering engine to perform medium-frequency displacements.