The Magellan AO system will begin commissioning in early 2012. Its VisAO camera will provide 20 mas FWHM images with mean Střehl ratios of ∼ 0.2 in R band on a 6.5m telescope. Depending on seeing conditions, Strehl ratio may reach temporary peaks as high as 0.5 at these wavelengths. To take advantage of these brief periods of high performance, we plan to adopt lucky imaging style data taking and reduction techniques. As part of this effort we have developed a novel real-time frame selection technique, which will use AO system telemetry and a fast shutter to limit CCD exposure to these very brief moments of higher Strehl. Here we describe the expected benefits of our frame selection techniques in various operating modes. We also present the results of laboratory characterization of the shutter, and describe the performance of predictive algorithms used to control it.