You'd just need a video switcher with live key capability that can accept a HDMI input from the DSLR. The other problem, though, is that a Canon 60D doesn't output a clean HDMI feed. The 60D HDMI output still includes the menu settings and record light in the feed. If you're willing to hack the firmware of the 60D you can look at something like Magic Lantern to get you around that problem, but be aware that this is a completely an at your own risk solution. Magic Lantern is not supported by Canon and if your camera suffers any problems as a result of the firmware it will not be covered by your warranty.