pumping from the top with a plastic tube/siphon type thing?
I have seen some of those available for fuel, not sure how well it would work for heavy oils. If you could find one capable, and you could get the tube right the way to the bottom of the sump I'd imagine you could get just as much out as you could by draining from the sump.
A tip (from someone who has never done it) might be to use a larger diameter tube at first, and then switch to using a smaller diameter tube to get the last bits, otherwise you'll get that slurping sound like when you're trying to get that last bit of coke out of your mcdonalds cup past all those pesky icecubes lol