I have had to do this.
I called Apple and asked them to re-queue all my purchases. They were nice about it and explained that it would be a one time deal and that I should be backing up my purchases. It was a good experience.
Every item I have ever purchased from the iTunes store appeared in my iTunes download queue. I did some math, realized that I would be downloading for weeks and would also exceed my ISP monthly bandwidth quota. I freaked out a bit and decided that I spend way too much money on digital content. After the crying, I decided that the files that were missing were not worth the time/effort/expense to recover in this manner.
Note: Every iTunes client associated with the account, that is set to automatically check for downloads, will try to download the media files. I have three Macs, it was maddening.
I called Apple and asked if they had the ability to selectively add purchases to the queue? I was informed that they do not have that level of control and that they cannot remove "everything but music". Apparently, they can manually remove items, but it really is a manual process. The CSR has to add and remove check marks.
In the end, I asked the rep to remove all items from the queue.
Perhaps this will all change when iTunes becomes a cloud based service? I hope so