I dont think advanced pay is sensible. What would happen if you failed the course half way threw and got RTU'd? You would have to give a weeks worth back. Better to do pay on an individual to get paid for the days you attended.
For example: someone who gets paid weekly but doesn't get paid by his employer during Camp.
In the days of Pay Parade, we'd have the option of taking one week's pay or two weeks' pay at the middle weekend. Most took both weeks' to avoid the risk of the cash getting lost in the system (which it often did).
I can't see why Advance of Pay should be difficult. It gets signed for and, if overpaid due to non-attendance or whatever, gets debited from following payments. Obviously, it's a privilege, not a right, so it wouldn't be offered to someone of questionable honesty. A bit like a 1033 for money.
There used to be a 'Camp Advance' whereby a part of the annual bounty was paid in advance, at camp, and was intended (I think) to offset the loss of earnings resulting from attendance at camp. Don't ask me how it worked, coz I don't know.
So in the past it was definitely possible but now... Who knows?
Anyone can get an Early Payment in Cash (EPIC) which is the same as an advance of pay. We give our personnel EPICs half way through camp just the same as we did in the past. If you need an advance before camp it is just a case of getting it authorised by your RAO or PSAO.