Ethanol doesn't cause carbon buildup. If you are referring to on the backsides of the intake valves...the only thing you can do to reduce future buildup is use a catch can on pcv side and valve cover vent side.
"Because ethanol does not burn as cleanly as pure gasoline does, it tends to leave behind debris in the forms of gum and a “varnish” in the engine and carburetor. These build-ups can lead to the most expensive effects of ethanol. With excessive build-up, your engine can fail. While carbon does eventually build with the use of pure gasoline, the use of ethanol can greatly speed up the process."
Pretty much most of our US based 93 octane gas Premium is up to 10% Ethanol. I run a Top Tier gas from Costco (also Shell, Exxon, etc.) which has more/better detergents in it. You really won't be able to make much use of it unless you have a tune (I run the LAP3USA Stage 1.5+ ECU tune, highly recommend it).