All these responses are weird.
Last year I asked at 2 different bike shops about upgrading my Sora/Tiagra stuff to 105. They both said the same thing - you cannot mix and match 9 speed and 10 speed equipment. If you want to put 105 components on a bike with 9 speed, you would need to replace the shifters, derailler, chainring, chain, and cables. So - everything.
I dunno, but that's what 2 shops told me.
I've heard of people finding the old 9-speed 105 and Ultegra shifters on ebay and putting them on, but that's it.