Work in a DV timeline.
Cut the HDV edit footage into a DV timeline (copy and paste your existing edit) and let render overnight. Done.
Any new HDV footage you might cut in needs to be rendered, but after the big downconvert (all done while you were sleeping) it’ll be only a little annoying. All new DV footage will cut right in and playback without rendering.
You absolutely WILL NOT need any new equipment or capture cards.