Dimz,
My suggestion is twofold:
A fighter who is sideways, as you describe, has less of a foundation to absorb the impact of your round kicks. You might consider kicking to his leg in this situation. Even if he "blocks," the impact that you give him will disorient him physically and psychologically.
Secondly, it sounds like the technique that your friend uses assumes that his opponent is just going to stand in front of him while he does this. May I suggest cutting an angle, by which I mean moving closer to him, yet at an angle off to the side, so that you are a)directly out of his line of fire, and b) in a position that he's not expecting you, leaving you an opportunity for an offensive. Especially consider cutting an angle to his back. KNEE 'IM IN THE KIDNEYS!
