All you need to do is ask when you book! After all, you're just asking for the lady to be dressed a certain way! At most MPs, the ladies have different outfits available, and somethimes they will lend outfits to other girls.
The other thing you can do is buy the SG outfit for the lady that you want to see. I've done that a few times. A petite lady like Mya or Chloe at HFH or Jenna @BP would fit into a girls size 14 or 16 (Chloe likely a 12) which would set you back about $50 at a place like the Bay or Sears.