I don't see any benefit to intentionially leave a gap at the valve, and I don't think the gap we've been talking about is due to lack of tubular cement, it's just that the tire is a bit stiff when first installed.. One of my fellow Classic Rendevous members posted quite a while ago that he leaves about a three inch unglued area opposite the valve, to facilitate getting an "extraction" started while on the open road and need arises to change out a tire. I don't recall who it was, however.

But yes, with tape it should be that easy to create a gap. I would say, mark the edges of the gap with cheap masking tape, run the tire tape from the valve to the mark, snip it, and run from the valve the opposite way until you hit the gap marker, and ship again. You just want to create a short place on the taped rim bed where the tire has a little extra response to when you grab it and push, after getting a flat.