It's an interesting theory generally speaking (willing to give it a shot here), but I'm not the most confident it will work personally.....Gas prices here as of this morning are $1.15 per Litre......do the conversion & that's $4.35 for a U.S. Gallon or $5.22 of an Imp gallon ...and will continue to rise as we get into the summer months.
The best advice I've heard (short of taking public transit, or switching to a more fuel efficient vehicle) is to combine your errands, look far down the road to aviod hard stops, drive gently on acceleration & keep your vehicle properly tuned & tire pressures at their correct level.....stretch out that tank of gas. B)