You can use your existing shifters with moustache bars. They will mount horizontally, rather than vertically; and this will change the hand motion required to shift, but it will still work. I cannot predict whether you will like it; I used to love moustache bars but for various reasons am not using the one I have now.
+1 and I've used Ergo shifters (not STI) on moustache bars before.
+1 for not using them now.