Welcome to ecomodder.
If you haven't seen it already, have a look at what Vekke is doing with his 3L Lupo
http://ecomodder.com/forum/showthrea...-2l-18235.html
You could steal some Lupo-specific ideas from him.
I suppose the tyres are already at a higher pressure ?
An air dam may also be a good and simple addition to your mods.
With so much of its time spent on the motorway, aerodynamic mods will give you the most benefit - weight isn't as much of an issue on the motorway.
Though not very civilized, that 1.4L VW TDi Triple is a great engine.
My sister has one in her Skoda Fabia, and it gets great fuel economy despite how it's being driven.
I have no trouble getting it under 4L/100 km or better than 59mpg US / 71 mpg UK.
I've had it at a sustained 105 mpg US @ 45 mph, totally unmodded, so you're not near the limit yet
