I think the best way to handle this is to simply keep track of all of the expiration dates of the miles and make sure that none expire. If any will expire within 6 months, then use Idine, worldperks mall, or another of the number of things that can add some easy miles to the balance and extend the expiration date for ALL miles in the account by 3 years from the last transaction.

That way, when you do finally get enough in any program you can redeem in that program.

Hilton used to be a good way to launder miles - 10k HH points for 5k miles, if you had 5k miles and nothing to do with them, but those doors have closed for all of the big six airlines except AA.