Urgent question about "Guaranteed to pass" for cars!

When I failed the smogcheck my mechanic told me that I should put in Guaranteed to Pass into an almost empty tank, then put in 9.1 gas (yeah right, as if I'm getting the most expensive gas with those fuel prices...) and drive it for 30 miles.
But on the package it says that I should fill it into a full tank (no mention about gas quality), then drive it to low and refuel.
My question is, since my tanks is half full (regular) can't I just put it in like that and drive around till it's empty? Since my registration expired after getting some stuff fixed I really shouldn't drive around much so I'm looking for the fastest solution.

thanks!

Welcome to AF, How can we answer this, you can't drive to supposedly clear up a condition you have not mentioned, yet you must for this miracle product to work!

I'm assuming your emissions readings are borderline, hence why your mechanic is suggesting a fuel system/carbon cleaner.

He probably recommended the highest grade of fuel because the premium fuel generally has a better cleaner/additive package than the standard fuel. The hope is that the cleaner combined with a tank of premium will help to clean better than just the cleaner by itself.

I've never seen an in the tank cleaner help a car to pass an emissions test. A few borderline cases have been solved with an induction system cleaner like SeaFoam, but I wouldn't expect miracles. Be prepared to spend some money to fix your issue. Drive the car hard while the cleaner is in the tank and get the oil changed before you retest. Make sure your car has fully warmed up before retesting.