@Roland Voigt: I think, in the interest of the game, that it should be assumed that a pass on 5♣ is indeed the result of some mannerism by the 5♣-bidder. As Benoit points out though, the double might save the day.
Come on! I find it offensive that you should have to pass 4♠ with this hand. Partner is showing a 5♣ sacfrifice, bidding 4♠ on the way. The real question is wether partner is allowed to pass 5♣. Without screens it's likely doubtful.