the only way that i know is like (R L') F2 (L R') U (R L') F2' (L R') U' (comm notation: [[RL':F2],U]) which for a 3x3 would be something like M D' M' U M D M' U' ([MD'M',U])
this is why I would rather do whatever-the-4x4-looking-megaminx-thing-is-called rather than a megaminx BLD