It`s not a straight fit as the PCD on the Mini wheels is different to Fiat(4x98).
I can`t remember what the Mini is, but if it`s 4x100 you can probably get them fitted with some "wobbly" bolts.
The size itself shouldn`t be a problem, but it depends on the offset of the wheels.
There are some easier alternatives and you probably be better of going for a Fiat fitment.