I'm gonna sound daft here, but I wonder if you have short enough sides (I'm thinking a less than half-a-cm), if you could use a cardboard stencil and an electric clipper? Never tried it...perhaps I will sometime - see if my idea makes a mess of my own hair. :D I suspect getting the sharp, clean edge round the design would be tricky by yourself.
But yeah, I still reckon the only way it'd work well is if you get someone else to do it.
I've yet to find someone who says they do their complicated side-designs themselves. I can manage stripes fine though myself, even round the back with the help of mirrors, but anything more complicated I've not tried.