You can do this now...
Though if you have alot of contacts it could be a tedious task to setup, but once it setup you wouldnt need to worry about it pulling over the ones you dont want
Heres how to do it.
Open Desktop Manager
Double Click Intellisync
Click on Configure PIM
Highlight address book and click on Advanced Settings
Click on the Filters tab
here you can create filters which you can configure to filter any email address (or any field) out of the sync.
Now whatever you setup it will ONLY sync those items matching your filters
so open up the contacts you dont want to sync and add something to one of the fields you dont use
then use the filters to sync everything which DOESNT contain something in that field.
Click this link to see what I mean about the filter http://www.blackberryclub.com/album_pic.php?pic_id=10
Hope that helps!