OK I didnt know that @Hoodini , heres some pro tips from an old greenhouse grower.
Get some mirrors or some mylar shiny reflective sheeting and use it to angle the light towards your plant.
You know the 12 volt sol sticks etc would run off a car or truck battery
Seriously we used to use big boards with a pivot on the middle and covered in a mirrored finish to angle the sun to the plants inside the greenhouses.
You could use something like a sheet of tin foil & make it into a bigger circle than the cup, place cup in middle after making the tin foil circle into a dome, place dome upside down you have a lovely shiny reflective sun trap.
Or get a bike / cycle with a dynamo put lights on the front, put an axle stand under back wheel, and pedal away shining the light at the cup.
I have actually looked into the new lithion battery packs that get charged up by solar panels through the day and release there charge in the dark hours when required to, bloody expensive at the moment though.
Alternatively you need to go creep onto the farm at ReikoX's place to pinch some of the unicorn poop. I thought he had started to sell it in bottles now I Have not seen it in the shops in UK yet though.
Best of luck Hoodini