As it seems, this capability is not difficult coding-wise, it just hasn't been implemented (yet).
Until then, the easiest way still seems to load disks from the menu, it just takes a few seconds anyway :-)
@matchaman if you use lr-nestopia you only use one button. L1. And you can map it to select. Select will still work the same. If you are in actual gameplay and you hit select it does not eject+ flip while you are in game. But if you say hit select once in gameplay when you get to the flip disk screen it will give you a disk side error. All you have to do is press the select button one time and it will correct itself. If in game you hit the select button an even number of times like 2x, 4x, etc... it wont give you the error. Not a big deal when you do get the error as you only flip a disk once or so while playing so you lose maybe a second of time. Again you need to switch to lr-nestopia as this does not work in lr-fceumm
@Caustra if you are talking about dvd rom drives and stuff then you would at the minimum mount the drive. You need to mount a dvd drive everytime you put a disk in it. To have it mount on startup you need to put a command in startup to do so. You need to open /media/ and add a folder called cdrom. Then you need to tell the system to mount sr0 to that folder. I can tell you how to do all that but because it does not show up as a usb i dont think it will work.