So it looks like it's a winner. I have yet to write a simulation for the case of a control group, but I have no doubt the method will work. Meanwhile, at the bottom of this page I have run a short simulation to check that the formulae for confidence limits and intervals adapted from the Becker formulae are correct or accurate in this case. But if reliability is practically perfect, as it often is, the degrees of freedom are effectively unaltered. For lower reliability, use of all four standard deviations in the effect-size calculation will make the actual confidence interval less than that calculated.
Someone needs to work out an adjustment for the degrees of freedom.