This is a partial answer dealing with only one type of lettuce: There is no way I know of or have heard of to remove the bitterness in iceberg lettuce. There is a way however to avoid buying a bitter head of lettuce, which I practice:
When shopping for lettuce, I take use my thumbnail to make a wide scratch at the cut stem and smell it (use anything to make the scratch - the idea is to expose fresh unexposed cells). Bitter lettuce is detectable by smell and can be rejected.
I have rejected whole bins of iceberg lettuce in the USA as bitter and used alternative types.
In the USA, the lettuce is now mostly wrapped in plastic at the grocery, requiring the peeling back of the plastic to scratch the stem.