I realize this doesn't help you now, but maybe it will help someone else in the future. The screeners I've dealt with are usually very understanding about wanting to hold your laptop out of the x-ray until just as you are about to go through the metal detector.

This has happened few times when I've flown, the last one I can remember was at SEA in October. The lline to go through the metal detector was long, and a lot of folks were pushing their items through the x-ray, then queueing for the metal detector, and letting their stuff wait for them on the other side. I loaded my stuff up to the start of the x-ray belt, then stood there with my hand on my laptop. The screener started to push it through the machine anyway, and I politely said "I'm sorry, but I have extrememly sensitive data on this machine and I can't let it out of my sight for more than a moment while it's going through. I'd like to wait until the backup right now clears."

He was fine with that- I stood there 10 seconds, the queue for the metal detector cleared out, and I went through & grabbed my laptop back from the x-ray. So, while it is true that I have sensitive information on my laptop, it's all encrypted, and it's not a huge huge huge deal if I lost it. So I kind of white-lied. I've done it everytime there was a back up, and never been challenged on it- I just really don't want to go through the hassle of replacing it and everything on it, and there's not control over who takes what off the end of the x-ray belts. YMMV, but give it a try next time- just wait with the item at the start of the xray, feed it through & go through the metal detector, the wait for it to emerge from the x-ray. If you're polite about it, I can't see it being a big issue.