So you want to spread your message with spraypaint, but you don't want your designs to be held back by worrying about pieces of a stencil connecting? Just use some cardboard, wire, and duct tape and you're ready to do the "impossible."
Here I took Aphex Twin's symbol off the ol' Interweb and converted it into a vector drawing with Illustrator. I then cut the design out of cardboard with a laser cutter. You probably don't have this costly bit of gear at your place and neither do I. I just make do with what others are kind enough to let me play with.
The low-tech version would be to print out the design in reverse, tape it to cardboard, and go nuts with a box cutter or Xacto blade. But that's another story for another Instructable and you're smart and clever enough to figure it all out, right?
After you've made your cuts, put all the pieces back together. This is how you're sure the placement is right.