Subdivide your folder with two folders. In one folder place you project you do not want to see. In the other folder place all your other projects (and add new projects to this folder). Then select this folder to be shown in your perspective.
Main Folder
↳Sub Folder 1
| ↳Project 1
| ↳Project 1
| ↳New Project
↳Sub Folder 2
| ↳Project to hide
The result would then be the one project you do is never seen in your prospective, but the other projects are including new projects add to the folder.
I answered a similar question in this thread.
http://forums.omnigroup.com/showthread.php?t=29630