If you've ever seen Chinese celery, it also is pretty much like lovage. I suspect that celery may have been seen mostly as a medicinal herb, rather than as a vegetable, but then candying such an herb would be a fairly likely method of preserving it and maximizing its medicinal qualities. Many candies were developed, essentially, as pills and lozenges. Failing those, in an emergency, I suppose you could use celery seed. The difference being that L. grows quite tall and does not develop the large spatulate stalks that celery does.
Lovage has a rather strong celery taste and can be quite bitter, use it sparingly.
If you cannot find L. use a little extra celery seed or leaf as suggested before. BTW L. can also carry a little coriander flavor, somewhat sharp and metallic, so you may consider a combination of Celery, Coriander and Parsley to best imitate Lovage's flavor. It's growing outside my window and I couldn't remember what it's name was, except that it was culinary. Lovage was used extensively in Apician recipes and provided a significant flavour to the overall taste of the foods it was used with. I have since used it in different capacities.