Good point. There doesn't seem to be a graceful way to do this yet.
One way to accomplish this is generate the sculptmap, save it to disk. Then, edit the image in photoshop or something similar and flip the image horizontally. Save it. Then you can load the flipped image in SculptGenMax and paste it into the scene to create a sculptie with flipped normals.
Another way to accomplish this is to apply an Unwrap UVW modifier to the sculpt in 3ds Max. Then, edit the UV Map and flip the entire UV map horizontally. Then, generate a sculptmap from it. And paste the new sculptmap back into the scene to create a sculptie with flipped normals.
I'll put this on my list of issues to look at in the future.