Yes, this is what happens when you put a bottle of grain alcohol into a toilet and set it on fire. Ronsonol/Zippo fluid makes for bigger flames but it leaves carbon marks on the porcelain.
My suitemates and I conducted a whole series of experiments along this line while living in the dorms in college. These were performed on a urinal rather than a commode, but the concept was quite similar.
Our tests involved Ronsonol/Zippo lighter fluid (with which we also performed other flammability tests*), acetone and methyl ethyl ketone. A roommate whose work/study job was in the chem lab was helpful in acquiring these test materials.
Our results concured with the Isosceles studies as regards lighter fluids. As I recall (these experiements were conducted approximately 20 years ago, so memory may not exactly serve), the lighter fluid left light to moderate carbon residue on the urinal. This carbon residue wiped off easily.
The flaming acetone test resulted in heavier carbon residue. This residue was also easily wiped off.
The methyl ethyl ketone test gave the most dramatic results. It produced a very heavy carbon coating over the entire urinal. This resulted in an entirely flat black urinal, which result we referred to as the "Negative Urinal". Further, the carbon residue proved to be highly resilient and the expirimenter's initial efforts to remove it proved unsucessful. We were unable to undertake further efforts to remove this carbon residue because time constraints prevented further efforts at that time. Upon our return, we discovered that the urinal had either been cleaned or replaced by the custodial staff.
* If you are interested in reports of any of the following studies, please contact the poster:
Study 1 -- The effects of Ronsonol/Zippo Lighter Fluid upon various makes and model of paper airplanes thrown from a third floor balcony.
Study 2 -- The effects of Ronsonol/Zippo Lighter Fluid upon a roll of toilet paper thrown from a third floor balcony onto a second floor balcony.
Study 3 -- The effects of Ronsonol/Zippo Lighter Fluid upon a roommate when squirted into bathroom floor grout and thereby channelled under the stall wall and lit.
You may also be interested in the Clogged Sink of Nastiness experiments, the Bottle Rocket trials and/or the Garbage Can Half Full of Water protocols.