Converting forward walk into a diagonal walk

I'm trying to turn a forward walk animation into a diagonal.  For this, I take the delta Z position from the final frame and use trig to get the new X & Z delta, ie Z.Sin(45) & Z.Cos(45).  Using Curves, I use the blue bars from the positional data to smooth down the Z motion, while for the X motion, I set the final frame position to Z.Cos(45) and then have to remove all frame positional data in between the 1st and last frame.  This results in a small amount of motion being lost and the character seems to slide around a little.

I'm converting rotations to Euler Interpolation for rotating the character, however I don't think this has any bearing on the positional data.

Is there a better way to do this perhaps?