I would direct you to a conversation on the ccp4bb last year ( https://www.jiscmail.ac.uk/cgi-bin/webadmin?A2=CCP4BB;eb55b86e.1003 ). Don't ask me how I remember this but what you are looking for specifically is found in this reply by Artem Evdokimov.
"It's called cross-soaking and it is a fairly popular technique
especially in the industrial community where we sometimes have to work
with hundreds of ligands.
I've done it on several occasions and mostly have been pretty happy
with the results. Having said this I also would like to point out that
soaking is not always the same as co-crystallization in terms of the
ligand-protein interactions. An extreme case is shown in the paper
below (figure 5):
http://www.iucr.org/cgi-bin/paper?sx5059
PDBID: 2i4g, 2i4h
Cheers,
Artem"
Hope this helps,
Katherine