So how do you prove "intent"? The only way the law works is by 1) prove the intention was to hide a controlled substance, 2) or that it was hiding a controlled substance (which is already illegal). Arresting on "intent" is basically charging someone for a crime before they commit it. That is what is vague about this law. It also, as written, only has the purpose of making something that is already illegal more illegal. A much better wording would be:
"Any person convicted of possessing a controlled substance, that attempted to hide the controlled substance in a hidden compartment, shall also be guilty of a misdemeanor(or felony if you want) of blah degree, blah, blah, etc..."
Also, "visible residue" has such a range for personal interpretation that officers are just going to take the shotgun approach and arrest anyone that has a hidden compartment. Which seems to be the case in the example in the OP link.