It doesn't actually combine the signals from the two sources, does it?

You might be able to build something using the video multiplerxers from MAXIM.

There's been lots of chatter about signal quality, etc, but once the switches are in place, i.e. once they've settled, the signal has certainly been indistinguishable from a single connection on the manual switch I still use on one pair of PC's in the corner of my lab. While they may radiate a bit, using ordinary relays, possibly small reed relays, might be worth a try.

Those MAXIM video switches look promising, though I haven't looked at them in quite a while, as they'll be much easier to shield. It seems to me that there are single-package triple switches available. Someone must have been thinking R-G-B. The SYNC signals are, ISTR, LVCMOS-compatible.

RE