What I found to be useful is the 409 stuff u clean your kitchen with. You can basically wipe AS5 and other thick thermal compound by applying a wet towel and using a twisting motion to clean it,
I used to wipe it horizontally and vertically but it just spreads farther apart, if you apply firm(but not too hard) pressure on the thermal paste and twist it, the stuff comes off instantly. I used anything from Pine-SOl to water and they all worked fine.