I actually considered getting a very, very large endmill to handle this sort of situation:
because of similar difficulties with smaller V endmills, but my first run was disastrous in terms of vibration, so I’m giving up on that (though I have an RC-1141 in my cart which I will try next, since it seems roughly equivalent to the RC-1148 which we sell which has worked fine for me).
My recommendation would be to draw the stock up in profile and work out how much insetting needs do happen and to what depth each layer would need to be cut and add additional layers until things are cut to the desired level of finish.
See:
for the technique.
That said, the ability to cut on the diagonal is the one thing which I really wish Carbide Create had (that and scripting — esp. if the scripting would be such that it would allow for programming diagonal moves)
Or, model in 3D using Carbide Create Pro and use a fine stepover/small tools.