Staying at the aria in a week or so. I know it has a key card check to get into the elevators. As I am at a conference a lot of my colleagues will be at the same hotel so don't really want to be see wandering the hotel with a lady on my arm. How do you discretely get around this

You choose will a plan !

You can easily meet us in a discreet spot and just hand over a key card. Then we can go up behind you.  

Meet somewhere in the hotel that is not crowded slide her your room key she waits a few minutes and goes up after you.I would recommend highly reviewed ladies in this case
No worries...us ladies know how to get around many gents are here for business with colleagues in the same hotel and need to be discreet

Rather than going down to *meet* the lady to slip her your extra key card..and risk being caught by your co workers who might be walking about.

the security just wants you to wave a card around, they aren't 'checking' anything. I've been out without my key several times...just joined up (trailed very closely) to a group of folks going down the hallway and strolled right by them as part of a group. Easy.

They have security BEFORE you get to the elevators.

That doesn't work if you're a hot chick by yourself.
They have a keen interest for confirming your legitimacy

...on my last visit I stayed at Elara. They have elevator security where you hand your key card to the security staff who inserts it into a reader. I assume the reader displays the registered guest's name 'cuz I think I recall that the guard said, "Welcome, Mr. Drumsticks. Enjoy your stay." I would like to have someone I've seen before give me a wake up visit without having to meet her prior to the visit and hand off the access card. If I leave an envelope with the card at the bell desk I have to place her name on the envelope. The lady, I would think, would have to show the staff her ID before being given the envelope. It's not likely that a lady will give me her true name and if I place her Provider name on the envelope, it won't match her ID, if asked for.  

You have a private message

Usually you must show proper ID to get anything from a front desk.  A lady had a big problem with that a while back when an envelope was left for her at the desk with her handle instead of her real name.

cancel your reservations and stay somewhere else.

Makes sense. I don't have that problem. lol!

Exactly never stay at the same hotel as co-workers

become friendly ($) with the bellman personally, as opposed to the belldesk in general.  have him hang on to it and describe the provider to him and her time of arrival.  when she arrives have him hand her the key. obviously explain this to your provider in advance.  
the valet may be a good point of contact for this, as well.