Plugin Help Ranking up feature

Alright so I'm trying to use BetterAlias in addition to Permissions Ex to create a command called /rankup
I already have a rankup ladder created and working, however I do not know how to do two things:

1) How to get Better Alias to call a /rankup command based off of /pex promote and pass that to the console, because as of right now if say I'm a Member trying to go up a rank, me calling /rankup returns a "Promoter doesn't have high enough rank to change