Bukkit

My administrators are able to promote regular users to the Moderator group.
By this we use the commands:

- /pex group Mods user add <name>
- /pex group Mods user remove <name>

To save them from typing this I wanted to alias the commands as:
/promote = /pex group Mods user add
/demote = /pex group Mods user remove

So they could perform:
/promote YepImRobbie
/demote YepImRobbie

But once attempted states:
'Error in command syntax. Check command help.'

The plugin I am using for promoting and demoting is PermissionsEx. How can I go about getting this to work?