A more cost effective strategy would be to replace Venture (which carries an annual fee) with (example) Citi Double Cash (no annual fee).
Venture "miles" have a fixed monetary value of $0.01 each. Earning Double Miles is just a distracting way of saying that Venture rebates 2% in the form of credit which can only be used for travel. Citi Double Cash rebates 2% in the form of money which can be used for anything.
You would use Skymiles to pay part of the ticket cost, then Premier Rewards Gold to pay the balance (and earn three points per dollar). Use the money from Citi to help pay the American Express bill.