Backing up iPhoto Library with DropBox

I moved my iPhoto library to DropBox in order to have a complete online backup of iPhoto (in addition to my local Time Machine backup and my SuperDuper bootable backup). The backup took a while since I have a large iPhoto library (20,000 photos, about 80 GB). What happened was that the size of the iPhoto library doubled on DropBox to 160 GB. There are a number of reasons for this (I found it too late), primarily because DropBox doesn't handle the symlinks well and creates duplicate copies of the photos in Folders called Originals, Modified, and Masters. Also my computer slowed down when I added a lot of photos to iPhoto, as it was syncing literally a couple of thousand files for every 100 pictures I added.

It seems like what I could do as an alternative to backing up the entire library is to just back up the Masters Folder to DropBox. However, I can't move the Masters Folder out of iPhoto to DropBox without breaking the iPhoto Library structure. I think I could use a symlink from the Masters Folder to DropBox, but I am not exactly sure how to do this (or whether this would work). I could also do some kind of automator script to copy the Masters folder to DropBox, but this doens't seem very efficient. I have scoured the web forums on this issue, but just don't see a good solution. It seems like a pretty fundamental issue to people with a lot of photos in iPhoto.