If you have drop bars, why don't you just buy a set of hooded drop bar levers, which will look a lot better on drop bars ? You will gain an additional hand position on the hoods, and will be able to operate the brake(s) from either the tops or the drops.

Also, FYI the bar is 25.4mm only where the stem clamps to it, and is 23.8mm elsewhere. So, you should be able to use any lever with a 23.8mm clamping diameter anywhere on the bar, including the flats on top.