What you are talking about is called Empty Movie Clips. You will need to use the attachMovie() command for this. It is fairly simple really, just a bit of coding and can be horrendous when you have a ton of MCs, but it is your project not mine
Any way, you said you already gave the linkage to each MC in the library, that is good, you will need to know the linkage names for this. here is the code:
obviously emptyMCName is the name of your "dummy" MC on the stage, linkageName is the name of the MC you want to load there, newName is the name you will replace linkageName with once it is created on the stage, and this.getNextHighestDepth() just tells it to go on stage and be visible.
_root.emptyMCName.attachMovie("linkageName", "newName", this.getNextHighestDepth());
You can put this on a button or what have you. Play around, it's fun