we need to use both their full name (in an email to field perhaps or on the front of an envelope) but just their firstname in the salutation

Bod, though I know nothing of your (superb) business, it won't stop me from offering some free advice.

If you're politely allowing them to enter anything their heart desires in the "Your Name" field -- and further assuming you're not being overwhelmed by a huge volume of registrations -- how about simply storing their preferred "Your Name" in your database ... and then later manually editing your new registrations, checking for goofs (and rude Turkish words) ... but also to manually enter a nice "salutation" field.

Parsing human names is one niche where I suspect humans still outperform computers, as I discovered years ago when my company sent out a letter to "Dear Captain Cruises" after the computer program incorrectly derived a salutation from Captain Cook Cruises. :-)