An alternative approach in case you don't have Joker skill (since it's a very situational skill, and one might not necessarily have room for it in their build) is as follows: (assuming you have the smooth talker skill)

At this point, you have entered the bathroom and killed the bathroom guard in a panic. Take a second to breathe. You now have 4 wandering guards, lobby guard, and cameras, with only 3 pagers and a dominate. We have established that yon don't have Joker, so you can only take care of 4 guards.

The plan is as standard: Kill 3 wanderers, dominate 1 (however you want to accomplish this), the only caveat is that you have to ignore the lobby guard, break the cameras, and throw the paintings to the roof (you *do* have the transporter ace, right?), where your other crew members are waiting to catch them (or, if you are doing this solo, carry them **very carefully** through the bathroom. ***DO NOT*** throw them into the bathroom). Do note that the lobby guard tends to spot people on the roof **extremely** quickly, so stay far away from that skylight. Hug the walls and you should be fine. Have the crew van the paintings, and sneak out through the bathroom.

As I said, this is a very plan-b approach, and it leaves one guard in play, but it's definitely doable. It just requires a little more care.