You can marginally increase runtime - and by marginally I mean seconds per tank - by placing an exhaust gas cooler in the pressure line between the pipe and the tank, it helps lowering the fuel temperature in the tank by a few degrees.
The concept was originally applied by onroad guys who were struggling to finish qualifying sessions without refueling and needed those extra seconds of runtime.
Just search for it in the forum, you will find a lot of discussion about the subject, but the consensus appears to be that it's effect is little and even less felt in offroad racing