Not level how? Are they wavy or do they slant off to one side?
For a wavy floor you can either let the base ride the crest of the waves or scribe the base over the ridges so that the top stays true and the bottom follows the contour of the floor. IF the floor slants off to one side, installing "level" base would probably telegraph the problem, making it more noticeable than letting it follow the floor.
I suffer from CDO ... Its like OCD, but in alphabetical order, LIKE IT SHOULD BE!!!