If you want to convince people, you have to argue what you believe to be true, and be seen to be convinced yourself.
If your message is: "Tell us what you want to hear, and we'll play it back to you", you will be seen to be shifty and unreliable. And rightly so.
Labour-aligned people who have back Leave should be treated with respect, and given honest arguments. They know that Labour has been pushed, bit by bit - by steady rank-and-file pressure on the reluctant leadership - into a de facto Remain position. Labour opposes the actual deals negotiated with the EU and supports a referendum which