One of the main reasons the frying is faster is because of the hot oil gets into the body cavity and frys the turkey from the inside and out.
read that again and tell me if it makes sense.
thinking about it, the only time that will change in the process is the recovery time for the oil once you put the bird in. Once it comes back to temperature, everything else would be pretty much the same. Theoretically, the cook time is the same (or very near the same) because the thickness of the meat is not changing and you're only minimally affecting the surface area of the breast (only the additional breast bone cut area is exposed). Everything else on the bird pretty much remains unchanged. I would have no hesitation on doing it (provided you solve the unbalance issue of only putting half a bird on the frying rack thing). Like you said, the whole point of the oil is to completly surround the bird (oil just = more efficient air). So if you ask yourself, "could i bake half a turkey" and the answer is yes, then you can do the same with frying.
and when in doubt, instant read thermometer saves the day.