The only ways I have seen for this are
1. Wear heels with all your costumes. If it's a costume with boots (like organization XIII) MOST people wear heeled boots.
2. The other person squats a little. This I have seen a few times.
Other then that I don't really know..
Cosplay DA Regular DA
Kumoricon 2014 (so far):
-Sora (Kingdom Hearts 2)
-Serena (Pokemon Y [It's the one I have lol])
-Akaito (Vocaloid. Black & Red Ver.)