In the Shield Safety & Instruction Manual, the official name for the slidelock lever is the "Slide Stop". The implication is that it can only be used to stop the slide, not to release it. Furthermore, the Manual (page 18) states that chambering a round is to be accomplished in the following manner:
"Pull the slide to the rear and release it, allowing it to carry fully forward. This strips a cartridge from the magazine and seats it in the chamber of the barrel."
No alternative method is given. Had Smith & Wesson wanted the slide stop to be used as a release, it would have been designed as such, and it would have been much easier to use for that purpose. For better or worse, the "slingshot method" is the only correct way to release the slide.