Some plate carriers don't require plates to be inserted to work as a stand alone chest rig. You can probably adjust the rig to work without the plates and then readjust once you have plates in the carrier. I understand the desire to make the rig fit properly as if you had real plates but for the cost of fake plates you could probably buy one of the less expensive real plates on eBay.
I haven't worn plates for several years now even though I have several carriers that allow plates to be worn. I will be buying several sets of plates to fill out those rigs as I am getting into more non static training. In my expriance the more you wear a properly adjusted rig with plates in it you quickly forget that they are in it. The old motto of train like you fight is true for everything you do in a training cycle your equipment is no different.
Some people will do skanky things for $25, and not all those people are crack whores.
San Jose, CA