If what the words meant to them doesn't matter, then they will mean whatever the majority wants them to mean to mean in any given generation, which means what they mean to you only matters this time.
Which means you aren't really making a constitutional argument; the establishment clause is just a convenient text for making the same argument you would make if the clause had never existed.
While I realize that in some circles it is popular to try and divine the intentions of the drafters of the document and ascribe different meaning to the words by channeling their spirits (ala Shirley Maclaine), it is more appropriate to ascribe plain meaning to the words.