None of the classic food preservation techniques will work for you. They are about having the food stay edible, not stay beautiful.
Most fixation solutions will work, but you probably don't want to keep them around your house. For example, if you filled the bottle with formaldehyde, it will not only be a major problem should it break in an accident, but I'd be also worried about anything which might seep through an imperfect seal - it is highly volatile, and neurotoxic and carcinogenic already in the ppm levels.
The one good way I see to do it is to use man's favorite poison: alcohol. Fill the bottles with ethanol until they are fully submerged. In principle, drinking alcohol at 37.5% will do, but in this case, the stronger, the better. Just use medicinal ethanol, it's also cheaper because you don't pay taxes.