there are at least 16 different language uses that are included in the term “figurative speech”.
saying Jesus used figurative speech at the last supper is nearly meaningless and is either intended to be misleading or is being used by someone who lacks command of the English language and does not realize the many different ways in which speech can be figurative.
which use of language are you referring to benhur when you describe the Lord’s words as figurative speech? symbolic usage, metaphorical usage, understatement, irony, etc., etc. etc.? perhaps you mean, when you say figurative speech, any kind of speech except literal? that is not a very precise, scholarly or supportable concept in my opinion, and by its very imprecision and vagueness makes a response impossible.
taken in context, everything about the Last Supper indicates the Lord was speaking literally. there is nothing in the accounts that indicate He was using any type of figurative speech. if you cannot believe that Jesus willed a miracle, of course you have to land on saying He was speaking figuratively (although as I pointed out earlier, that is nearly meaningless since figurative speech has myriad ways of being used).