I just found out about NuGetPowerTools: https://github.com/davidfowl/NuGetPowerTools
Also see: http://blog.davidebbo.com/2011/08/easy-way-to-set-up-nuget-to-restore.html
Update: NuGet 1.6 now supports Package Restore: http://docs.nuget.org/docs/release-notes/nuget-1.6