Question

How do I specify a payout provider for an associate in custom code?

Answer

Using two options:

IMoneyOutService.AutoProvisionAccount (creates account and assigns to Associate)
IMoneyOutService.SetActiveOnFileMerchant (assigns associate to certain provider without provisioning account)

This conversation helps describe the problem and solution:

When someone signs up how do we know what money out merchant they are going to use? If you have two money out merchants one for the US and one for Europe. when someone enrolls I need to send them to the correct money out merchant.
I'm not sure. There's probably a way to do it now. We don't have a method that just does that last part. Wouldn't you just hook submit_application and call this method with the right merchantId?
but I don't have the Associate Values yet. That is the exact reason I need it
Then you would call IMoneyOutService.AutoProvisionAccount which would set the values and make it active
I do not want to create their account (in the money-out provider's system) until commissions are earned.
Then SetActiveOnFileMerchant would work, and you pass in some default or empty associate values