In order to verify on behalf of an eligible person (for any group), you must be a dependent of that person.
If you are able to produce a document of proof from this person, you may be able to proceed with verification. Depending on the group, documents are proof are uniquely identifying documents a non-eligible person would not have access to.
For example, any kind of image which could be acquired on social media can't be used as proof. This would include trinkets, medals, awards, uniformed photos (when applicable), etc.. Good examples of uniquely identifying documents include official badges, ID cards, pay stubs, and signed letters from employers.
If you're buying this item as a gift, and can't produce any uniquely identifying document of status, unfortunately you wouldn't be able to proceed with VerifyPass.