MOLLE Plate Adaptor
This will allow you to either mount on a modular dropleg, or on a vest.
MLS 15 or
MLS 16
As far as I can tell, these just push through the MOLLE loops and hook under the bottom.
IMO, the MLS 15 would be my choice, since it gives you full range of directions for mounting your holster (vertical for leg mount, horizontal for chest mount).