That image is making me giggle.
Have you searched ThinkGeek? There are all kinds of goofy geeky gifts there. There are too many toys there that I want myself to list, not to mention geeky fashion accesories.
Last year, I got my little cousin a plush Nyarlethotep doll, wrapped in a classic-style gift box. I also did some shopping at The Bone Room, for said cousin and my grandfather. (Relax, I just got 'em fossil castings. And some bug candy.)
I also built my uncle a model of the Aerial Steam Carriage. It had about a three-foot wingspan.
This year—well, I did some shopping at Unitednuclear.com.
Your sister might like something from Archie McPhee. It has nothing anyone NEEDS, but plenty that people would enjoy.
Well, this is ALWAYS a good gift idea!
It says adult supervision necessary. Most of the adults I know would need supervision while using that thing.