I also would advise keeping it just about friendship for now without any expectations for what may come. Let things happen naturally and don't try to force them considering his neutral response to your confession of wanting more.

I will tell you from experience how difficult a transatlantic relationship is. I was in one for about 2 years with someone I met here actually (me US and him UK). We also started out as close friends but we skyped everyday as friends and both of us had a desire for more. We saw each other about 5 times during that period (each visiting the other at various times). As a couple we continued to skype everyday for hours usually. Even with all of that, to say how hard it was is an understatement.

So seeing as you are starting from a lesser point than we did, please take the difficulty into consideration as well as overcoming his neutrality with this. Stay grounded and rational which it seems like you are able to do. It's the best course of action.