It would probably take 4 but I think that if I was going to do that then I would put an aux fuel tank in. the two containers i have are are 1 gal each and are only there in an emergency. There are larger fuel containers but the little ones I have will do (at least until I can afford the aux tank) Hopefully my maths would not be too far out from a reasonably close distance to fuel station.
I have used them once on the ST1100 when attempting to ride between Cobar and Broken Hill, ran out of fuel about 15Km from the Hill. It was a good learning experience in underestimating the 110Kph speed limit and windy weather conditions
An interesting point you raise with the IBA limits.