We have several public forms that we only allow known anonymous users to submit so we don't get spammed and the general public submitting specific forms.  On those forms we want to put a link to a separate contact style form and pre-populate some of the variables on the contact form.  I use a custom HTML field that looks like this....

<a href="https://ehire.lasd.org/Forms/contactsupport?Applicant_ID={/dataset/Applicant_ID}&amp;Applicant_Email={/dataset/Applicant_Email}" target="_blank">If you still need additional help, open a help desk request by clicking here</a>

Generally we email them the link similarly with fields pre-populated so the variables will be there on form load....I think.