I reckon 5 actually, lay two down side by side and another two on top, passenger seat out and another.
Or 6 add one in the engine bay.
Or 7, remover drivers seat and use it as a seat for the journey, only if less than 10 miles though
You can easily put a 2.0 RS lump into your 1.2, In fact, there are companies who do it for you.
For example
http://www.k-tecracing.com/show_product.asp?id=2098
The only issue is the cost, it isnt cheap at all. You might as well sell yours and buy a 172, and you will get everything else, interior etc etc/
I want some of what your on!! But you'll have to inject it between my toes my mom checks for track marks!!