Well, I decided that other people may benefit from this too, so I've added a "-fast" option and released ExifTool 6.24 with this new feature.

With the -fast option, ExifTool won't check for an AFCP or PreviewImage trailer on JPEG images.

And what's this about the -htmlDump option not working? I thought you meant that it didn't exist in your version, but it should work fine from version 6.00 onward. Let me know if you have any problems with it.