Most extracts have alcohol in, which can be very drying even in small amounts, so I wouldn't advise it personally.
I buy essential oils from the aromatherapy section of a chain health food store. I use a lemongrass one, which smells quite strong initially but fades quickly once it's in my hair and leaves it more or less odourless.
Maybe something else you could add would mask the smell, if not as strongly as essential oils? Maybe crush and boil down some actual lemongrass and add that. Some of the ingredients that get added to FSG as standard can help. Add a bit of coconut oil instead if your hair responds well to that, which will also add some extra moisturising properties and I find smells quite strongly of well... coconut. (Go figure.) Some people add honey, which I find leaves it with a very sweet smell, if you like that sort of scent.