Browsers don't seem to let you simulate key presses.
The simplest way to get text to the clipboard would be this js, but it still requires the user to press ctrl-c enter.
"window.prompt('Copy to clipboard: Ctrl+C, Enter', 'what');"
All other solutions I've tried aren't working or are IE only. One that I haven't tried is ZeroClipboard which uses flash to access the clipboard, but it still requires the user to click. Also since it uses flash it won't work on android/ios.