Paypal - 'Capture' payment when status changed

[addedlovely]

With Paypal Standard (the built in Paypal gateway), when 'Payment Action' is set to 'Authorize' - changing the order status to 'complete' or 'processing' does not result in the payment being captured.

Looks like this could be possible with the Paypal API, and would be consistent with the Stripe gateway behaviour - capture_payment();

Logged on ideas board:
http://ideas.woothemes.com/forums/133476-woocommerce/suggestions/3945761--pre-authorize-only-checkout-for-paypal-and-stripe

WC Version: 2.5.3
WP Version: 4.4.2