Here's my dilemma:
I'm working on a documentary that is heavily reliant on a dearth of stock footage, netted from all corners of the stock-supply chain.
We also have a ton of original footage shot in HD @ 1920x1080p.
In order to work in FCP7 we have been using ProRes timelines, and have been up-resing all of the comp stock footage to ProRes (Proxy) so that we won't have deal with rendering. However, as you may imagine, this is leading to a large problem with storage space.
I suppose it would be possible to down-convert all the original HD footage and work with a lighter codec, but the director and editor like to see the what they can in its full glory.
Is it possible to use another codec in the ProRes timeline that would play nice? Or is that just it? Once you're in, you have to render to play nice? (Is this something that happens in X, and possibly Premiere as well?)
The bottom line is, if you work with mixed formats inside your sequence, you will have to render in order to see your final product - no way to stop that.
I am a little bit confused about your setup though. You are saying that your ProRes Proxy files are what is filling up your storage? If that is the case, I would highly consider just picking up another FW800 drive to store some files on.
Recently, I had 100 hours of ProRes Proxy 1080p30 footage show up from a studio in Latin America. Total size = 2.7TB. We literally just plugged in the RAID and let it play from there directly. Worked like a champ, since ProRes bitrates are so low.
There are no technical solutions to creative problems. Only creative solutions to technical problems.