Alright. Case closed.
Thank you Yaost and Linkdex for providing logic, but ended up writing everyting on my own.
For those seeking the same thing: it is hard to have their box work with a random custom form, as it was constructed to work with the admin-side form. Yet is still possible to through their text-check functions in the above mentioned files, and see how it works. If you know php even at mid-to-low level, I believe you will be able to understand and re-rewrite what you need.