If (at the gate) an MVP Gold with a companion was not in FC on an award already, and I tried to sell those FC seats and had no takers and all other MVPs and Golds were already in FC (or had declined to be) Id upgrade a Gold and companion complimentary. Its happened before (believe it or not!).
Otherwise see below:

(Found under the Q & A on Mileage Plan at Alaskaair.com)

First Class Upgrades
Paid Upgrades


Paid Upgrades may be available within 24 hours of flight departure through Web Check-In, or on the day of departure at the following Alaska Airlines airport locations:

* Check-In Kiosk (with Credit Card Only)
* Departure Gate (with Credit Card Only)

Award tickets and Bonus Travel Tickets are not eligible for paid upgrades. Paid upgrades are subject to availability, do not include stopovers, and exclude industry discounts. The link to upgrade to First Class during Web Check-In will only appear if First Class seats are still available for purchase. Upgrades can only be used in conjunction with Value or Full Flex fares. Prices are based on one-way trip miles, as shown above. Value and Full Flex fare categories are booked in Y, S, B, M, or H classes of service.
Mileage Plan™

Redemptive Upgrades

* Require 15,000 mile redemption for one-way travel systemwide on flights operated by Alaska Airlines.
* Can be used in conjunction with Value or Full Flex fare categories only.
* Redeem by calling Alaska Airlines Reservations at 1-800-ALASKAAIR (1-800-252-7522).
* Effective June 25, 2008: Available within 24 hours of flight departure through Web Check-In, or on the day of departure at an airport Check-in Kiosk.

Mileage upgrades are booked in "U" Class and exclude free, tax/PFC only, award travel, industry, promotional discount or two-for-one fares. Mileage Upgrades can be used in conjunction with Money & Miles (AS50) Award Tickets. U Class may not be available on all flights. Value and Full flex fare categories are booked in Y, S, B, M, or H classes of service.
Complimentary Upgrades

MVP® and MVP® Gold members, can reserve or waitlist a seat in First Class on Alaska Airlines (subject to availability).

MVP Gold
Unlimited First Class Upgrades Anytime on Y or YAS fares (Full Flex Fares); 48 hours prior to departure on other fares. Anytime on qualifying fares booked in Y, S, B, M, H, or Value and Full Flex fares; 72 hours prior to departure on other fares.
Unlimited ability to upgrade one person into First Class when traveling with you.

Complimentary upgrades are booked in "U" Class and not available when traveling on award tickets, including the Money & Miles (AS50) Award. Upgrades are subject to availability as "U" Class may not be available on all flights.