FileResult getting corrupted

[thinkbigsoftware]

I'm using this package for the first time with Umbraco 7.3.1. The DonutOutputCache attribute is on a controller which is registered as the default controller in the application.

I also have a RenderMvcController which uses route hijacking to override the default controller and serve a file as a FileResult (normally a pdf). The problem I'm having is that the caching is still intercepting the request and causing all file downloads to get corrupted (I've tried multiple file types)

Is there any way to get the donuntcaching to ignore this controller entirely?

Thanks very much