I've never been able to reach all the places that need to be sprayed with a spray can. The little red tube that comes with it just isn't enough. Here is my solution.
Step 1: Acquire Tubing
Go to a hobby store that carries gas type engines and get apiece of fuel line tubing. You need the size small to fit the spray tube, and since its for the fuel of the engines it should handle most all spray products.
Step 2: Conect Tubeing
Take the spray tube that comes with the can, holding firmly, press the fuel tubing over one end. It will take some maneuvering and will fit snug, about a 16th of an inch is good. Now plug the cans tube into the nozzle.
Step 3: Attach Wire
Get your self a sturdy piece of wire like cloths hanger or bailing wire about as long as the tubing and bend a small loop in one end for a handle. This will make it easier to maneuver. Strong enough to hold it's shape but easy to bend. Tape or glue this to the free end of the fuel tubing, and a couple more places along the wire. Be careful not to use a rubber band or something that will constrict the flow.
Step 4: Ready to Spray
Now your ready to go! Just bend the wire to the shape you need to get the spray where you need it. The tubing is soft and flexible and follows the wire. Just watch so it doesn't snag or touch hot spots.