The real trick of your scenario would be to see if the spread reflects the change between the two contracts during intraday moves. I don't have access to exchange-traded spreads from my broker, so cannot see it's movements. But I've seen a few charts over the years from others, and they just don't seem to move all that much, no matter the underlying action.
Today would be a good example to pull up, as I noticed the ES went down around 40-45 points at one point. So if you have access to any ES spread data for today, check the PA of any of those spreads and look for a large spike-up. I'm guessing you won't see much of one at all, and coupled with the uber low margins of a near-dated spread, you're looking at only $10,000 margin on a 40-lot, so you have a lot of wiggle room with a 6 figure account.
