Our ops manual does not mandate it, I am pretty sure the flight manual doesnt either, but our policy is load from the front as it leads to less problems and our company CofG calcs are based on that assumption.
with no pax you can only be sure that with north sea fit that they will be in limits up to 1000 fuel and you will prob be OK up to 1100 subject to calculation, if you want more fuel than that you need to carry ballast/pax and load from front for max effect.
regards
CF