Sub Projects

How easy it would it be to implement sub-projects?
I've only recently started using SimpleGTD but one of the things I plan to use it for is helping to plan my wedding - this includes a lot of mini projects such as finding a photographer, planning the honeymoon, sorting out invitations etc. etc.

Rather than cluttering up the projects list, it would be nice to have "Wedding" as the main project with everything else on a collapsable branch underneath.