Yes, exactly. You can use plaster bandages (you can find it in creative stores) or pour some plaster on your latex mold.
For example, you can do that way :
Take a piece of glass (I'm using an old mirror).
Fix your master on it (double sided tape, or putty)
fill the gaps with plasticiline or other putty (you dont want some latex between your master and the mirror)
Put some talc on your master
Make your coats of latex to make your mold, for big pieces, you can make an "armature" of medical gauze, for exemple.
Once it's done, put some talc on the dry latex
Pour some plaster on it (using a "box" made in cardboard, lego, etc...) or make a "plaster bandage" on it.
Once everything is dry, you'll be able to keep your mold straigt, and minimize the usual problems with latex molding.