With a Customized Portal 2 Level
After seeing how much his girlfriend enjoyed playing Portal 2, Gary Hudston contacted Ellen McLain, the actress who provides the voice for the game's villain, GLaDOS, and asked if she would record some special dialogue, because apparently she was in the phone book. McLain agreed, and Hudston hired some people on a Portal modding site to build an entire Portal 2 level for him using McLain's custom dialogue. Hudston had his girlfriend play through the level on her birthday, which ended with GLaDOS delivering Hudston's proposal, because nothing says "I love you" like a homicidal AI.
Presumably his original plan consisted of HAL 9000 reciting the lyrics to "Pictures of You."
When he's not tearing up at love stories like the manly man he is, Colin also writes for his college newspaper, braves the jungles of fan fiction, and thinks of the big questions, such as "Why is this your business?"