Set the number of shards to keep outside of a Soul Bag, using the Options frame (accessable by typing /sshards). Then all shards recieved over this boundary will be removed.
If there is space in your Soul Bag's and shards in your main bags then these will be moved into the Soul Bag's.
1.1b - Released
1.2b - Moves shards from main bags to empty slots in soul bags. Changed wording in options (thanks Tekkub). Maximum value of options slider is now the number of slots in your bags.
1.3b - Should work now, Removed AboutPanel
1.4b - New Soul Bag checking code, WotLK fixes.
1.5b - Fixed issue with assigning incorrect variables.