You don’t want to do this. The GAL is just a representation of Active Directory – to simply add people will mean you need to create mail enabled contacts for them all, and while that can be scripted, it is a pain to administer (and a nightmare to use).
What you may be able to do, is to instead use a public folder. Export your data to CSV (or whatever) and import these into outlook as contacts. Drag them over to a public folder, and now all users will be able to get at it (and anyone you choose can administer it.)