With a store bought cheese, it's harder to get a pure culture. Here's what you can try:
Open up the cheese. Dunk it in at least a 70% alcohol solution for 30 seconds. Then rinse with water. Sanitize a few knives, and cut all the outer edges of the cheese to expose only the insides.
Before this, boil some skim milk, and let it cool down to about 90 degrees. take the inside of the cheese you exposed, and put it in the milk, then take a sanitized fork and mash up the cheese with the milk. Mash it up so there are no big chunks. Cover up the container so it is sterile, and leave overnight.
The next morning, dump the entire thing into the milk with your culture, and proceed as usual. At the end of the cheesemake after you remove the cheese from the mold, rub it with coarse salt. Then rub with salt every other day for a total of 3 times. Then age it in such a way as to expose the most surface area. Blue doesn't like damp, but it does like high humidity. Aim for a 90-95% humidity. 100% may lead to other molds competing.
That should help give you an active blue mold population. Inoculating the milk gives the blue a foothold so it grows quickly. Rubbing with salt helps to control other molds. Just remember with blue you need to be very sanitary. It's easily contaminated.