Using Application Pages for List Forms

I'd like to use an application page that I created in the _layouts folder as the new document form for a document library in SharePoint.

When I attempt to do this in SharePoint Designer, I have to browse to the file but it doesn't let me browse to the _layouts fold开发者_开发问答er.

This functionality will be list specific so is there a way to make this connection on a per-list basis? My only idea right now is to use a redirect page.