Take a look at Yukon.  Yukon is a premix of Permit + 4 oz/acre rate of Dicamba.

I don't know if that would be enough for the prickly lettuce - that would somewhat depend on the size of the prickly lettuce.  However, the Yukon will take out the nutsedge just as well as the Permit, and should help on the lettuce.

I don't know if the Impact will help enough on the lettuce to use it.

You don't say, but I am guessing this is non-RR corn?

I'm thinking while writing here..... I wonder what tank-mixing some atrazine with Yukon would do to that lettuce???

I might have to think on that a bit......