Here's one from the Instructables website: Insert two innertubes, one deflated, in your tires. If you get a flat, just remove whatever caused the puncture, then pump up the other tube.
On the plus side, the cyclist won't need to remove the wheel, remove the tire, etc. You know the drill. All that's needed is a pump.
On the minus side, the author explains that drilling another hole in the rim for the second innertube's valve stem might weaken the rim.
Please check out the instructions on the website before you try this at home. This might be geared more toward mountain bikes or hybrids instead of road bikes. It's also going to make your wheels heavier.
A query to your local bike shop might not be a bad idea either.