Create Displacement/Height maps from Normal maps???

Hello everyone, 

I looked online and seem not to find a answer to my question. Is it possible to make a displacement/Height map from your normal map on SP? Heres a example; you purchase a premade high rez basemesh that includes texture and normals but would like to use the high frequency details from the normals in zbrush but zbrush does not use normals maps. So now you need to convert the normals map into Height/displacement maps and how would you go about doing so in SP? I hope to hear from your soon and thank you in advance.