You can very much combine an Amex 2-for-1 voucher, a GUF2 / 2 * GUF1s, and a Joker if needed to make the avios seats appear. I've done it a few times, always on the phone though
For bonus marks, also through in an ex-INV or ex-JER to dodge the APD, and hear the shock from the GGL team agent on just how cheap you've managed to get your redemption
