You would probably save more weight by leaving the spare at home. What is weight of the car? The interior bits might save 25 kilo. Run it near empty and bump the tyres up to 34 psi.
But i reckon you might be wasting your time and effort mate as to make the weight loss worthwhile the car will get defected. If the compliance plate says five seats, the cops expect seating and seatbelts for five. And don't say they wont pic you , those P plates are a magnet to cops eyes. Especially if you are "going a little harder".
Not having a go but learn to drive in a granny car, then let loose in something that is capable of doing what you want to try. Rollas are great beasts, but they are not speed demons and the handling can be suss. Cheap to run, cheap to insure, reliable, and a shitload of parts around.
Smelly