@Grant Hulbert, I was also an early supporter and never had the impression there would be multiple simultaneous sensors supported. The spec always listed one sensor input port. It does, however, sound like a nice feature for a Twine 2.0!
Here's a simple IR beam-break project I found online. If you wired this up exactly as-is, the output triggering high should map to the input on the Twine breakout board and achieve what you're looking for. I might have to pick up some parts and make…