They really need to keep Castle on the Cloud. That's probably one of the most thematically important songs in the show (remember whose picture that is on the poster).
Dog Eat Dog, Turning, the Waltz of Treachery and one of the "Valjean self-torture" songs they can cut. Lovely Ladies can just be truncated (like what they did to Little People). The Look Down reprise can be cut down to just instrumental music over scenes of poverty in Paris.
As sacreligious as it sounds, if they really HAD to, I feel they could cut the first Do You Hear The People Sing. Think about how powerful that song was if they just used it at the end.
Flaming begins in 3 ... 2 ... 1 ...