HTML5 Offline Application: How to view TIFF files from localStorage (FileSystem API)

I have a potential customer who wants an application that can download large amounts of TIFF files locally on a machine for display.

After having discarded Java apps and Windows apps as too difficult to distribute (he has no control over the client computers) I am suggesting an offline HTML5 application.

TIFF is only natively displayed by Safari, and the FileSystem API only works on Google. WebSQL will be too small for the amount of data required (3-4 GB).

I've looked at different plug-ins (AlternaTIFF and BlackIce) but both need to be installed separately, which most of the users will probably find difficult to do.

I am wondering if there was a local TIFF Viewer that I could call from the browser that would open the TIFF from the FileSystem?

If this does not work, the last solution would be a conversion of the TIFFs to something else on the server, but it's going to make my database double in volume.

Any suggestions would be welcome!