You have 3 choices.....
Lie , bite the bullett or get creative with choice of car.
No 1 is asking fot trouble big time . Its no use not declaring
mods- might as well not pay for the insurance since they wont pay a claim if you get caught
you said No 2 is out
So just leaves 3
What you want is a std car thats underated ideally a turbo or larger engine version of something which they dont think exists.
For example Nissan stageas have various 2.5l models some with half as much power as the normal one. The rare S us a totally different car which is so much quicker but the insurance people actually class them as a lower group because they are manual not auto ( no good for a young driver but the idea is the important thing )
I think the mitisbishi colt is the same -Im pretty sure there is an early imported turbo version with the same name that some insurance companies dont know about. They are more intersted in if its modded so getting an early std turbo car might be worth looking into .,
You could always get some quotes before you consider buying one,
Note I am not saying lie to them - just find a company that asks ( or doesnt ask ) the right questions