I honestly doubt that growing blue mould in cream for a few days will have much effect, but why not try, it won't harm you either.
Why is it not going to work? Mould needs oxygen to grow. When making blue cheese (or generally cheese with "internal" mould), holes are punched through the curd to create air channels to supply the mould with oxygen. A Wikipedia image of Gorgonzola clearly shows how the mould grows around one of these punch holes. You can also see how the mould only grows around other natural cracks in the curd, while there are large solid areas of cheese with no visible sign of mould at all.
If you don't do this and the curd is without naturals cracks, the mould will only grow on the cheese surface, like for example on a Camembert.
If you soak a piece of blue cheese in cream, some spores may of course dissolve and reach the surface, but they will only be able to grow on the cream's surface. Another problem is that Penicillium roqueforti is not growing particularly fast. Roquefort is for example ripened at least four months under ideal conditions, so just a few days will not allow much growth.
Why is it not going to harm you? Using harmless or perhaps even beneficial moulds like Penicillium roqueforti to prepare food is not only done for the taste, but also for their preserving functions. Or more precisely, different species of mould tend to fight each other, so seeding food with a "good" mould will prevent the growth of "bad" mould. Anyway, cream will get sour and taste bad long before dangerous amounts of mould would grow.