What a good idea.
My mother used to make Omlette au curé with young sorrel and dandelion leaves in early spring. It was said in France that it was the only thing they could afford.
Lovage is a wonderful herb. It's slightly reminiscent of celery, but only slightly, I think tastes are impossible to describe. I use a few chopped leaves in a green salad, also to flavour a plain Omlette, and lovage soup is wonderful. You would need to experiment with amounts as the flavour is strong and adjust to your taste.
A salad of bulb fennel, celery, sharp apple, yellow pepper and a few cauliflower florets with chopped lovage leaves scattered over is beautiful summer treat.