Swap Magic lets one play any discs but it requires the boot disc to be swapped after the bootup. There are Magic Key but it seems the web site is gone and the sliding card doesn't look appealing (may damage laser or spindle). The flip top can also work but the ones I found are black only, looks like no one made silver version? :suspicion: Would it work if I installed a switch that bypasses the internal lid down switch so it would always seem like the lid is never up unless I am playing multi-disc that needs lid-up to swap the disc? Maybe a normally-closed push button that I press to send "lid up" signal?
Disco Azul have what you need in stock if that's any use? http://www.discoazul.co.uk/magic-keys-4.html
Beware that there were several versions of the Magic keys. Your series requires v3, which I have. v2 and below are only good for older slimline consoles. I don't remember that the Swapmagic site allowed visitors to buy stuff directly from them while it was still up in 2007. I got mine from an online retailer, linker4u.
i have both version's. I stuck them all in a bag a while back and have no use for them since I mostly use modchips or fmcb with hdcombo or hdpro installed.
You have a scph-7700 why not just use free mc boot with ECR? Very few multidisk games dont work with it as most creates a save game , that can be loaded from disc2.