I did it a bit in reverse. Wired cash from my credit union to Tesla (via Wells Fargo), and got a loan preapproval from USAA for the balance and emailed the dealer form for that to Tesla to have 'the dealer' complete that paperwork.
Evan, Via Tapatalk
I planned to do the exact same thing as you (including the use of a USAA loan for the balance). Please let me know how it works out for you and any advice to help make the process easier.