I'm also looking into this challenge and you will need a 3rd party tool. I'm looking at these right now...
SDExplorer http://www.cloudstorageexplorer.com/
syncDriver http://syncdriver.com/about
Well, there's limitations but it's also free. I've managed to get around them by using SDExplorer (A little flakey; wish there were some better alternatives) and splitting large files into 50MB parts (smaller ones too as they usually go into an encrypted vault file that can be a few hundred MB in size).
It normally only allows you to sync, but you can also upload through the web interface. There is a program that allows allows you to load it like a folder and upload/download files without syncing. It costs $14/year but I think it's worth it.