I wouldn't bother boiling the addition.
I'd recommend using lemon zest, as it won't cause fermentation. Lemon juice will have sugar and cause fermentation, leaving only a sour taste behind. The oils in the zest will provide flavor without sugar (which is why we use orange peel for witbier!).
Some people use lemongrass, but the flavor is different so make sure to sample a bit before you add it.