We only index the known fields from a merchant's datafeed.
The only option I think you have is to replace the "Image" field with the URL for the large image within the Factory. To find that field, click the "more info" link for the products.
Or you could write some logic within your views to serve up the large image when needed. It seems the pattern for their images is this:
So, you could use a simple str_replace
in your views to substitute _m.jpg