I believe that if you take annual leave from your current employer and do the endorsement during that period, then you are technically paying for training and education that furthers your qualifications in the industry with which you are employed, therefore making a tax friendly ruling more likely.
If you resign from your employment, do the course and then take up employment with a carrier, you are technically not employed in the industry at the time of training and therefore the tax office may have some more ammunition to take a hard line.
I am no accountant, just going on my personal experience with the tax office and training about 7 years ago. Times change, and the biggest problem with the ATO is consistency. For one example, I had three separate rulings on one issue - 1st was yes, the 2nd no, and the 3rd was undecided.
Maybe the Feds should look into organising something whereby they force Virgin to employ you while you are training - even giving you a couple of hundred dollar allowance would satisfy the criteria of employment potentially.