Automated interpolation?

A simple question: is there any to quickly interpolate values for a certain element between two keyframes?
Allow me to put this a bit differently. Essentially, I need this:

Except that I already have a few keyframes in between to animate a different part of the picture, like this:

When I try to add in the slower animation of picture one, the keyframes in the middle already saved values for the elements in animation 1, so I get this:

So my question is: Is there any way which I can quickly have synfig calculate and rewrite the values for animation 1 at the waypoints in the middle without affecting the values for animation 2 and 3, and without having to rewrite them myself* or having to delete and recreate the keyframes in the middle, so I end up with this?

* Not exactly problematic when it’s just a single vertex, but when it starts involving several as well as tangent ducks, it gets kind of tedious.

There is probably a way to do this with exporting the animation or something like that, but it just doesn’t seem very practical for this particular purpose to me, especially since synfig is already able to automatically calculate the values when there are no keyframes.
I really hope there is a solution for this. Anyway, thank you in advance for any help on this problem.

And if there already is a way to do this and I just missed it, I’m terribly sorry for the trouble.

When working on animation 1 turn off the lock keyframes button and so they won’t affect the addition of the waypoints.
Keyframes are helper to animate but you can add waypoints without them.


… That is exactly what I needed, thank you very much.
I can’t believe I missed something so basic. I’ll have to read the manual more carefully next time.
Again, thanks.