I don't make bloomy rind cheeses very often, but when I do I just harvest while mould from a store bought brie or camembert. Just cut off the surface white bloom of a bite sized wedge. Mix that into some 25 C water with a sterilized fork. Mash it around and stirr until the water is good and cloudy. Then, just pour this liquid into the milk when you add your culture. I try and prevent any lumps from transfering but I don't think it matters.
This works just fine and isn't the cause of the slipskin (which is related to ripening too fast, usually prevented by lowering the temperature). However, it does mean an extra possible source for contamination. Don't use a cheese that's been sitting out, unwrapped, in your fridge or on the counter, etc. Buy a new cheese, open it, take what you need, eat the rest to destroy the evidence.
I've never had a problem with contamination doing this, just make sure you've steralized absolutely everything (i.e. the cup you'll mix the mould and warm water in; the fork you'll mash it with; the knife you use to take the mould off the initial cheese) and you'll be fine.