How would any director get two straight men to shoot a same sex bedroom scene?

The first bedroom scene in Blue is the warmest color, if it could even be shot with male actors, (physically I cannot see it done without exposing parts of the male anatomy most care not to see) how would a director or producer talk straight male actors into swap spit, groping each other, and to shove their face into another man’s crotch? If you were an actor what would they have to do, promise, or say to get you to do it? If it is true and neither Léa Seydoux nor Adèle Exarchopoulos are gay (maybe they are bi, I have not heard), then it can be done, I guess. Is it easier for women because they don’t have as much surface hardware down there?