I don't think there is any advice I can give that is definitely going to work in your situation. Every cuckold situation has it's own quirks and peculiarities. For us, my wife was naturally promiscuous. So I didn't have to 'convince' her. In fact, she just went out and did it and it was up to me how I reacted. Luckily, I was superaroused by it and I realised it was what I wanted.
You obviously want it too. What does your wife think?