The feature is available in Plesk 11.5, which is in preview stage now.
One can download it for evaluation, but it is not for production servers.
The download links are in Plesk 11.5 Preview thread
I am now in the position where I have to give a freelance support my admin account username and password...
Dear Alexey,
I have Plesk 11.5 installed but still cannot see the button in Tools -> Panel.
I'm not sure if this has something to do with it: http://support.powerdnn.com/kb/a465/how-to-create-secondary-administrator-account-the-plesk
FYI:
I can see that under Tools -> Additional Services "Mobile Center" is displayed 5 times.
Jon L:
That is no way to ask for help or submit a feature request. Please show a little respect. The admin user for the Linux version of Plesk is the same as the Root user for the operating system. This may require more development than either you and I are aware of, not being programmers.
More disrespect and nonconstructive criticism. None of this is going to help the feature come out faster.