Well if you're talking about lock screen as in "standby screen", it may be doable. If you're talking about "Security lock screen" (to prompt your security code), I also investigated this issue -and would be more than happy to provide a solution- but it's not possible, Aegis won't allow neither you nor a 3rd party app/shortcut to trigger a security lock.

If you think this approach is wrong -and IT IS wrong!-, please see, confirm & vote for this bug report: https://harmattan-bugs.nokia.com/show_bug.cgi?id=376