No one said it would be "easy". But it's certainly possible. And even if they got Lester, they still need to trade from their OF surplus. The formula's there, sign and trade, the issue is putting a name on he who shall be signed and he who shall be traded for.
It's also clearly not as difficult as you're making it out to be. There are available arms, and the Sox have money and surplus talent. Stop your slow and steady descent into the dark side.