I tried it today.
My passenger, "Bernie," fit inside, but had to stretch out to the end of the footwell, face first into a pillow. Buckled in for safety.
159 cm, not too bad a fit. The bindings were a problem, hence flipping the board over to be able to slide it under the shelf. It needed a little push up from underneath, in the footwell, to clear the footrest.
So a ski/snowboard day is possible in the Elise, without any sketchy roof rack set ups. Just a sketchy looking character sitting in your passenger seat.