I was delighted to discover SNesoid for Android, which has let me relive my favorite childhood games, particularly Chrono Trigger. But in 2300 AD, after spending a half-hour chasing a rat across the screen to extract the password from it, it looked like SNesoid wasn't able to support hitting the three necessary buttons together (L + R, then A). And then this Android Forum thread caused me to look into key mapping.
To enter the password and get on with the game:
1) Hit the menu button in SNesoid
2) Go to Input settings, then Key mappings
3) Scroll down and select Button A. When it says Press a hardware key... press one that doesn't already cause a change of state in the app (i.e., don't choose the "home" or "menu" buttons.) I went with the volume down button.
4) Go back to the game, and stand in front of the sparkling panel where you need to enter the password
5) Keep a finger on both the L and R "keys" on the on-screen keyboard, and then hit the physical volume down button (or whatever button you chose in the key mappings interface.)
And that's all! Go back to the key mappings interface and get rid of the key assignment for Button A, and head across the bridge discover that Lavos destroyed the world in 1999.
Note: I'm running SNesoid 2.0.4 on an Unrevoked Forever Evo 4G with Froyo. Your mileage may vary.
Additional dorky footnote: I loved Chrono Trigger so much that I made a mask of Mune in art class when I was 11, and spent hours playing the game and transcribing all the dialog in a Word file that I then used to write a novelization that inevitably focused primarily on Lucca, my very favorite character. Embarrassingly, in re-playing the game I discovered I can still quote back much of the dialog before even seeing it.