Can't add social profile fields to web forms

I’ve created an IS web form for our website to recruit guest contributors for our blog. Within contact records in IS, there are dedicated fields to store social profile URLs (FB, LI, Tw), but the web form builder doesn’t include these as field options to add to forms. A fair number of guest writer requests that we get are spam (probably not real people) and I’d like to force a LinkedIn URL field to confirm people are real and they actually would be qualified to write for us.

Is there any way to accomplish this, beyond adding a custom/duplicate field?

@Brody_Dorland, they are only open to the API. When will the Contact social fields be opened up to API? (Facebook, Twitter, LinkedIn)