I had a cluster blow in my 2002 - they said it needed to be "flashed" so it would show the correct mileage, but I wasn't concerned about the trip or the cost of flashing since it was just up the road.
Another option would be getting a Scangauge 2 - I know it has MPH and I just searched the manual and it does talk about "fuel remaining" - do a search of this pdf at this link:
http://www.scangauge.com/support/pdfs/SGMan5_1.pdf
That would be a ghetto way around it, but it might require calibrating the tank by going almost empty...and if you can't tell now - not sure how you will do that without carrying around a gallon of fuel for whenever you run out.
I'll have to check with my Bentley manual and see if there is anything about programming the cluster.