I can't get leafpad to start like that, without setting up /usr/bin or something.

If you just enter the name of the software you want to launch that does it for me. If you want to open a file with a programme then this can be quite good, e.g. "leafpad file.txt" However, some programmes are launched with names that aren't the same as their name in the application menu e.g. to open a new terminal window type "osso-xterm".
Also, be careful about shutting the terminal you used to initiate the launch because you'll close both at once - unless that's what you want. Not sure if you can spawn the new programme so it's uneffected by whatever goes on in the terminal.