The nicest solution would be to:
1) migrate blogger to use CR
2) use cr_item_rels and the <relation> tag as mentioned by Dave and Joel.
Any volunteers for this?
I'm contemplating thinking about moving pinds.com to a 5.1 platform, and this is one of the features I really want in my new site. And being able to actually use it on a daily basis is a strong motivator for adding features. However, the process of moving data to the new platform is going to be fairly painful ... :(