Apparently, TDI does have an option for nitrox cert strictly on line:
Online Nitrox Course
(Remote Certification Option)
You can complete the Nitrox Diver Independent Learning Course in your own hometown if you meet all of the following conditions.
you do not live within 25 miles of us or a local TDI facility, and
you are 21 years old or older, and
you are an advanced certified diver or equivalent.
Here's how it works.
Step 1. Complete the online portion of the Nitrox Diver Independent Learning Course.
Step 2. Print and fill out copies of the Nitrox Knowledge Review and TDI Liability Release forms.
Step 3. Fax or mail
(a) copies of the completed Nitrox Knowledge Review and TDI Liability Release forms.
(b) a copy of your Advanced Water Diver Certification card or equivalent proof of this level of certification.
(c) a copy of your drivers license or other proof that you are 21 years old or older.
(d) your Visa, Master Card, American Express or Discover credit card number and expiration date.
(e) a note authorizing us to bill your card $87.50 US plus $5.00 US for postage and handling.
Note: If you purchased a password online, tell us and we will deduct the amount you have already paid from the total billed to your card.
Fax to 561-451-4602
Or
Mail to:
American Dive Center
Attn: Peter Schulz
1888 NW 2nd Avenue
Boca Raton, Fl 33432
Upon receipt of your documents, we will review your paperwork for completeness and accuracy. We will then send you an e-mail noting your successful completion of the course, or additional input needed from you to successfully complete the course.
When all the paperwork is in order we will bill your credit card, send in the application for your certification card to TDI, and mail your card to you when we receive it from TDI.
The processing time from all of your documents approved to the mailing out of your card to you is typically about two weeks.
American Dive Center
8092 West Sample Road, Coral Springs, FL 33065
954.346.0174 in Florida
800.310.0174 Out of State
http://www.coralspringsscuba.com
Email
staff@coralspringsscuba.com