I agree via the pcv is next best way and if your lucky you local repair shop will at least do it through your PCV and not the main vacumm line. Either way is considered incorect by the manufactures of these products.

One preferred engine-cleaning method for an automobile engine involves first identifying a suitable vacuum port in communication with the intake manifold for application of the engine cleaner composition. The vacuum port should preferably provide a steady source of vacuum and should preferably be located downstream (but as close as possible) to the throttle plate. Ideally, the vacuum port should not be a restricted vacuum source or a "T" connect into a vacuum source. Manifold absolute pressure (MAP) sensor, positive crankcase ventilation (PCV), and brake booster vacuum ports should also preferably be avoided. In many engines, for example, application of the engine cleaner through the PCV or brake booster vacuum port may result in distribution of the engine cleaner to less than all of the engines cylinders. Preferably, the vacuum port source should provide a vacuum of about 16 inches of Hg or greater, more preferably about 18 to 22 inches of Hg. In determining whether a proper vacuum port has been located a vacuum gauge may be useful.