No problem! Microwave saves the day!
Just slice the top off a head of garlic, place it in a microwave-safe bowl. Drizzle with olive oil and sprinkle with salt and pepper. Add 1 1/2 tbsps of water to the bowl and cover with a saucer.
Microwave on low for 3 minutes, take it out and check softness with a fork. Microwave another 3 minutes then by 1 minute increments until you achieve the desired softness. You could broil the top if you want a golden roasted garlic but I didn't mind it like this.
So just squeezed out the cloves and mashed them with the potatoes, a bit of milk and butter.
I may never roast garlic in the oven again!