Pat has always pointed out to players on the Express that there's no point to solving prematurely because all they are doing is leaving money on the table. I am certain that a player who insisted on doing so (say, they weren't sure of a spelling of a word and didn't want to risk it; yeah, I know, it's Wheel, Jake) would be allowed to do it, but he's always couched it as "if you know it, why don't you call another consonant and make some more money."