If the theory is that something in plain lemon juice applied to the lips is somehow effective, this might work for some people.
However, I don't think plain lemon juice contains salicylic acid? I believe lemon juice has to be heated to get to the stage where it contains salicylic acid.
So, if the theory is that salicylic acid somehow helps as an EC treatment, there are easier ways to apply it to the lips.
Salicylic acid is a type of beta-hydroxy acid derived from willow bark. A natural exfoliant, it works by penetrating pores and removing excess dead skin cells.
You can make a very effective (and very cheap) salicylic acid treatment "mask" by dissolving a few plain, cheap, uncoated aspirin tablets in a few drops of water. Add just enough water to turn the dissolved aspirin into a spreadable paste. Then apply the paste to the area you want to exfoliate, let it sit for 5 to 10 minutes until it drys, then rinse it off with some water.
I have used this many times as a facial mask, and it very effectively removes dead skin cells and leaves your facial skin soft as a baby's bum. So I would imagine it could work similarly if applied to the lips?
[Note: You really have to use the super cheap, super plain aspirin for this, the ones that have NO coating on them. The ones with an enteric coating don't want to dissolve into a paste.]