Cam hoops are bottomless. Mine have 1/8th inch diameter holes. I wouldn't cut the bottoms off the ricotta molds, the should still do the trick.
You are saying that you have P.C. and Geo. That means that you're missing the main acidifier (like Flora Danica).
If that's true, then you won't get it from supermarket brie or cam since it's already dead at that point. You'd have to use buttermilk (or yogurt) and culture it... and at that point and given how tricky camemberts can be as a first cheese, you might rather do something else
If that was a typo, and you actually have the main culture (usually Flora Danica), then the supermarket brie/camembert's rind can help inoculate the P.C. You can just do a bouquet garni with as much rind as you want to spare and retrieve it from the milk before renetting. Or food-processor it with some water and spray it on the cheese later. In fact you could arguably wait until the cheese is done and your cultures arrive before spraying the P.C. on. Again, given how tricky a good camember is to get right first try, I'd probably try an easier one just to get the cheese bug going. I'd probably do Halloumi with cultured buttermilk... it's easy and foolproof, delicious, you can fry it and taste some straight away, age the rest, and do ricotta with the whey.
