I need to fit a length of coving along a wall that already has the
same coving on each end wall. Normally, I would mitre but that's not
possible with the others in situ. Nonetheless, it should work fine if
I cut it to the right length and scribe the right profile at each
end.

So what's the problem? Well, when scribing skirting for example, it's
(relatively) easy to transfer the profile as the face of a board is
close to flat, but the curve of the coving makes this damned near
impossible.

Does anyone have a clever trick for this, or is it just a case of
guess it and use plenty of filler when it goes belly up?