If you could make your bowels start doing photosynthesis then you might have a crack at it. Unfortunately your digestive system is only good for reducing compounds fed into it to extract stored energy not to do the opposite. It’s the equivant of asking what you could burn so that the ashes smelled like fresh pine needles instead of soot. Yeah, eating rose oil may make your sweat smell like someting different but I think your shit will still stink. Also remember that poo is also made of waste products from your body that are not directly impacted by what you eat.
Is this actually true? Does the human body actually move waste products out of the bloodstream and into the intestine? Or, indeed any products other than water and digestive enzymes?
Just curious, 'cause I thought not.
The Master speaks on “why is shit brown.” The material is not moved directly from bloodstream to instestine; there’s an intermediary step; but in general the answer to your question is yes.
Aren’t you worried about the bees?
That’s the first thing I’ve seen on the SDMB that’s made me laugh in the longest time. Bees and aphids would be a problem. And after a chili cookoff, you’d have to pass around the antihistimines.
I read an article in a medical journal once saying that if patients took large doses of Pepto-Bismol (which is chemically similar to the bismuth subgallate pills mentioned above) on a regular schedule, it would deodorize their intestinal gas by affecting the way their intestinal bacteria metabolize sulfur. They had some experimental evidence to back it up.
This would just make your farts stink less, not smell like roses, but I think it would be a necessary step in the process.
I’m not sure how to make your farts smell like roses, but I once read about people in the 1800s or thereabout taking something like pine-sap to make their pee smell like violets. Does that help?
John
It doesn’t matter if your farts smelled like roses; they’d still stink. Maybe that’s a subject for great debates?
Have you considered Attar of Roses Enemas? Guaranteed to get rose-scented material to your lower digestive tract without having it breakdown or get diverted along the way.
On the other hand, since things get absorbed into your bloodstream from the bowels (It’s how your body gets a lot of its water back from the digestive tract. And I’ve been told that they used to use enema feedings to keep patients going who had problems with their mouths back in the pre-IV days), you might want to take a really close look at what you put in there. Anything with lots of alcohol is strongly contraindicated.
Nice to see this thread has bubbled up to the surface again.
This may not be an entirely practical suggestion - but in the book Stiffs by Mary Roach, she relates an ancient practice by altruistic old Chinese men.
They would limit their diet entirely to honey. After awhile all of their, um, effluent would supposedly be honey-like. After a period of weeks-months they would die, and then be preserved in honey for many years, until they had formed a honeyed preserve, bits of which could be taken by grateful patients to cure a range of maladies.
It would give new meaning to your username, anyway. 
Just noticed that. I wonder how guests find such old threads if they can’t search?
I think it was linked in another recent thread somewhere.
Consume attar of roses, only $200 an oz.
As Seeker74 mentioned- Chlorophyll tablets. But just get 'em from a health food store, the brand named ones or the ones you get at a pharmacy are very over priced.
Stay away from Bismuth compounds- they will also make you constipated. 
In general- adding Probiotics (acidolpholus and it’s cousins, found in “live culture yogurt” and in pill form at a health-food store) will make your gas smell better. It won’t be the smell of rotting paleozooic swamp gasses anymore- but it won’t be roses either.
I am not a real Doctor.
Rosewater is a pretty common ingredient in tea and some foods in the Arab world. No idea how much you’d have to consume or if it’d have the desired effect…