Thanks! I was able to find multiple options that way (both via Lufthansa and Swiss Air). I was lucky because my original booking were three different flights with an open-jaw end (CDG-->LAX-->EWR-->LHR) so I think it's quite flexible.

Is the pricing that is used to determine the cost of the total fare (i.e. old segments + new one) or just the new segment?
On ITA matrix, they are all priced together at about half the cost of what I had paid for the original trip. But don't know if this is reliable or if I should also cross-check the prices by looking up the one-way F flights as well?